Preinvasive Endometrial Neoplasia


Hormonal field effects (non–atypical endometrial hyperplasia) must be distinguished from true precancerous lesions (endometrioid intraepithelial neoplasia [EIN]) because of their differing management. This chapter also presents mimics of precancerous lesions and includes special presentations of lesions with altered differentiation (metaplasias).


endometrial intraepithelial neoplasia, hyperplasia, metaplasia, precancer



The pathways to endometrial cancer are multiple but can be condensed into two major carcinogenic sequences, each with their pathologic correlates. The most established pathway is the one leading to endometrioid carcinoma. This route has a well-defined precursor lesion (endometrioid intraepithelial neoplasia [EIN]) that can be detected and treated in advance of malignancy. A second pathway leads to serous carcinoma, and a component of the transition to malignancy is a so-called serous endometrial intraepithelial carcinoma (EIC). The reader is advised in advance not to confuse this (serous EIC) with a precancerous lesion inasmuch as it may behave as a malignancy without invading the myometrium. This reality underscores the challenge of identifying the early warning signal (precancer) for serous carcinoma. As of this writing, precursors to serous cancer have been newly described, and the reader is cautioned that a diagnosis of a serous cancer precursor in the endometrium should not be made in practice without considerable discussion and qualification. The second part of this chapter will provide an update with some guidelines for dealing with this problematic area.

Precursors to Endometrioid Carcinoma—Endometrioid Intraepithelial Neoplasia


EIN is a clonal proliferation of architecturally and cytologically altered premalignant endometrial glands, which are prone to malignant transformation to endometrioid (type I) endometrial adenocarcinoma. EIN lesions are noninvasive, genetically altered neoplasms that arise focally and may convert to a malignant phenotype on acquisition of additional genetic damage. Diagnostic criteria for EIN have been developed by histopathologic correlation with clinical outcomes, molecular changes, and objective computerized histomorphometry. EIN is conceptually similar to complex atypical hyperplasia (CAH) of the endometrium, and most EINs overlap with CAH. However, as defined, EIN is not exclusive to CAH, and not all CAHs are EIN lesions. This is due to differences in classification criteria and an inconsistent application of hyperplasia diagnosis by pathologists, as will be discussed later.

EIN should not be confused with unrelated serous EIC, which is an early phase of type II papillary serous adenocarcinomas of the endometrium. This is particularly important from the clinical perspective inasmuch as clinicians must be made fully aware of the risk attendant to a diagnosis of a noninvasive serous carcinoma (serous EIC).

Historical Background

In 1949, Arthur T. Hertig, a pathologist at Harvard Medical School and Boston Hospital for Women, described adenomatous hyperplasia and anaplasia of the endometrium as precancerous lesions that may antedate the appearance of endometrial adenocarcinoma by 1 to 5 years. At that time, estrogens were recognized as participants in the promotion of endometrial carcinoma, but there were inadequate tools to resolve field effects resulting from systemic hormonal exposures from neoplastic proliferation caused by somatic mutation. This remained a major source of confusion and contention for the next 50 years, during which the pace of nomenclature proposals outstripped actual advances in the understanding of this disease.

A 1985 landmark paper showed that subjective cytologic atypia within a lesion increased cancer risk 14-fold, the single variable conferring the largest incremental endometrial cancer risk discovered up to that time. In 1994, the World Health Organization (WHO) sanctioned a classification system whereby four classes of hyperplasia were divided by architecture (complex or simple) and cytology (nonatypical or atypical). Atypical endometrial hyperplasias, whether of simple or complex architecture, were widely construed as premalignant lesions requiring therapeutic ablation. The dominance of cytology in risk assessment has since been tempered by the realization that pathologists are unable to classify individual lesions reproducibly as atypical versus nonatypical and by the recognition that architectural features have a predictive value at least as important as cytology.

A parallel effort to use computers to classify low versus high cancer risk endometrial lesions played out against this backdrop of pathologist-derived classification systems. The availability of software and hardware for computerized tissue morphometry in the late 1970s enabled a greater degree of objectivity in the histopathologic description of premalignant endometrial lesions than previously possible. When statistically modeled against clinical outcomes of interest, individual cytologic and architectural predictive variables measured in a hematoxylin and eosin (H&E)–stained slide could be discovered and validated. This reached its pinnacle with the development of the deviation (D) score, a morphometric scoring system with superb cancer-predictive performance exceeding anything seen previously. The architectural variable of volume percentage stroma, a measure of gland crowding central to the d score, has since been incorporated as a key subjective EIN criterion (more glands than stroma) that can be understood and interpreted visually by pathologists without recourse to a computer.

Microdissection of targeted small lesions in paraffin-embedded tissues has enabled a precise correlation between molecular genetic and histopathologic features of endometrial precancers. Molecular studies showing a clonal growth pattern for endometrial precancers have established their focality of origin and subsequent centripetal expansion as geometric properties of evolving lesions. By the time such clones can be seen under the microscope, there are evident changes in cytology and architecture that offset them from the background. Lesion size and contrasting localizing lesion cytology and architecture to that of the background endometrium are characteristics that must be assessed during routine diagnosis and have been incorporated into EIN diagnostic criteria.

A formal proposal for the EIN diagnostic schema emerged from the realization that the histologic changes seen in genetically altered monoclonal endometrial precancers were identical to those previously defined by computerized morphometry of H&E-stained sections as increasing the likelihood of carcinoma. A high degree of clinical relevance was immediately justified by a series of preexisting clinical outcome studies, all of which validated the cancer-predictive value of the original D-score–based diagnostic algorithm. Just as diverse and independent methods of discovery were integrated to define the group of lesions that we now know as EIN, this is an entity that may be diagnosed in several ways. For those with access to the commercially available QPRODIT software and morphometry workstation (Leica, Cambridge, England), EIN lesions are those with a D-score less than a threshold of 1, which identifies lesions with a 27% chance of concurrent or 46-fold increased risk for future endometrial carcinoma ( Fig. 17.1 ). Practical implementation of subjective criteria for EIN diagnosis by pathologists working at a standard microscope with routine H&E slides is the subject of the remainder of this chapter.

Fig. 17.1

Prospective cancer risk of an endometrial intraepithelial neoplasia (EIN) diagnosis. Long-term cancer-free survival of 477 endometrial hyperplasias was stratified by morphometry into high-risk EIN (d score < 1) and low-risk benign (d score > 1) subgroups. A total of 27% of women with EIN will have a concurrent adenocarcinoma diagnosed within 1 year of EIN diagnosis; 28 of these were excluded as cases of concurrent carcinoma. The resulting plot shows long-term cancer occurrences evolving from an EIN lesion, an event that is 46-fold more likely in EIN-bearing compared with non–EIN-bearing women.

(Data from Baak JPA, Mutter GL, Robboy S, et al: The molecular genetics and morphometry-based endometrial intraepithelial neoplasia classification system predicts disease progression in endometrial hyperplasia more accurately than the 1994 World Health Organization classification system. Cancer 103:2304–2312, 2005.)

Implementation of the Endometrioid Intraepithelial Neoplasia Schema by the World Health Organization in 2014

EIN diagnostic criteria were sufficiently different from those used in the 1994 version of the WHO four-class hyperplasia schema that a formal adjustment of terminology and criteria was required. This was implemented as a new standard in 2014–2015 ( Table 17.1 ) on recommendation of WHO and the American College of Obstetricians and Gynecologists. In the current two-class 2014 WHO hyperplasia schema, hormonal field effects are designated as “Endometrial hyperplasia without atypia.” Correspondingly, precancerous high-risk lesions, documented extensively as EIN, were so designated. One minor refinement of the WHO was changing the endometrial to endometrioid to clarify its relevance to the general class of endometrioid carcinomas (type I endometrial adenocarcinomas). One other nomenclature accommodation in WHO 2014, made to facilitate transition from their legacy system, is that the high-risk group of EIN may be synonymously designated as EIN or as “atypical endometrial hyperplasia.” As might be expected, diagnostic reproducibility improves when using the 2014 compared to the 1994 version of the WHO criteria because fewer groups require distinction, and criteria are better defined.

Table 17.1

Endometrial Intraepithelial Neoplasia (EIN) Diagnostic Schema

EIN Nomenclature,
WHO, 2014 a
Topography Functional Category Treatment ICD-10 Code
Endometrial hyperplasia without atypia (benign architectural changes of unopposed estrogen) Diffuse Estrogen effect Hormone therapy n85.01
EIN Focal, progressing to diffuse Precancer Hormonal or surgical n85.02
Carcinoma Focal, progressing to diffuse Cancer Surgical stage–based C54.1

a Modified from Zaino RJ, Carinelli SG, Ellenson LH, et al: Tumours of the uterine corpus: epithelial tumours and precursors. In Kurman RJ, Carcangiu ML, Herrington S, Young RH, editors: WHO classification of tumours of the female reproductive organs, Lyon, France, 2014, IARC Press, pp 125-134.

Despite the nonatypical versus atypical terminology option in WHO 2014, pathologists must keep in mind that cytologic appearance alone is insufficient to discriminate among these entities. Rather, new diagnostic criteria, unavailable at the inception of the now-replaced 1994 four-class WHO schema, must be applied, according to the published EIN evidence base. These include minimum size of localized lesions, objectively defined gland crowding thresholds, and comparison of lesional with background glands to identify significant cytologic changes. For these reasons, entities named in the 2014 WHO schema do not correlate absolutely with earlier 1994 WHO classes. Fig. 17.2 shows general WHO 1994 to WHO 2014 correlations based on the combined experience of multiple European and American groups.

Fig. 17.2

1994 World Health Organization (WHO) hyperplasias (four-class) rediagnosed by two-class endometrial intraepithelial neoplasia (EIN) criteria (same as WHO 2014). These version criteria differ, so the correlation is not fixed. The colored portions of the bar graphs show the approximate percentages of each 1994 WHO hyperplasia class that will be diagnosed as EIN. The remaining 1994 WHO hyperplasias not diagnostic of EIN ( yellow ) will be allocated to unopposed estrogen (anovulatory), polyp, and other benign categories. The pie chart shows the relative contributions of each hyperplasia type to the EIN diagnostic category in a biopsy series of sequential endometrial hyperplasias seen in a busy hospital practice.

(From Hecht JL, Ince TA, Baak JPA, et al: Prediction of endometrial carcinoma by subjective EIN diagnosis. Mod Pathol 18:324–330, 2005.)

The Patient at Risk

Endocrine Factors

Endocrine risk factors for endometrial precancers are essentially identical to those for endometrioid endometrial adenocarcinoma, with estrogens acting as promoters and progestins as protectors. In the Postmenopausal Estrogen–Progestin Interventions (PEPI) trial, 12% of women receiving unopposed estrogens developed atypical hyperplasia over the 3-year surveillance period compared with 0% of placebo controls. Estrogen risks are obviated by the addition of progestins such as medroxyprogesterone acetate, which protects against the development of endometrial hyperplasia. When administered in a combined low-dose oral contraceptive formulation, this may reduce the endometrial cancer risk below that of the population background.

Genetic Factors

Sporadic EIN lesions are precursors to the subset of endometrial carcinomas characterized by endometrioid differentiation, PTEN gene and PAX2 inactivation, and microsatellite instability. Precancer histology seen in women with a hereditary endometrial cancer risk go through a comparable premalignant phase of EIN, including PTEN inactivation. Hereditary nonpolyposis colon cancer (HNPCC), caused by abnormalities of factors involved in DNA mismatch repair, is an autosomal dominant condition conferring a 60% lifetime risk for endometrial cancer, generally of the endometrioid type, with more than 75% showing microsatellite instability and 68% having a loss of PTEN tumor suppressor function. These tumors occur on average about 30 years earlier than their sporadic counterparts, leading to a current management recommendation to begin annual or semiannual endometrial biopsies by the age of 30 to 35 years. A second heritable cancer syndrome characterized by an elevated risk for that type of endometrial cancer—with a premalignant EIN phase—is Cowden syndrome, caused by germline transmission of a mutant PTEN allele.

Early detection and treatment of premalignant endometrial disease is a mainstay of endometrial cancer therapy. The lifetime risk for endometrial cancer is 2.4% in the United States, primarily a sporadic disease driven by complex interactions between somatically acquired genetic lesions and ambient hormonal selection factors. Most endometrial cancers are discovered when the patient develops symptomatic bleeding, followed by a diagnostic endometrial biopsy. Under these circumstances, 21% of endometrial adenocarcinomas at the time of initial diagnosis have already extended beyond the subjacent myometrium, with extension to the cervix (stage 2; 5.8%), regional nodes or extrauterine tissues (stage 3; 7.7%), or distant sites (stage 4; 8.3%). If detected earlier, many of these patients could achieve surgical cure by hysterectomy alone.

Epidemiologic Factors

EIN has risk factors similar to those of endometrioid endometrial cancer. Specifically, women who are obese are at an increased risk to develop EIN. This relationship between obesity and endometrial proliferation is most likely secondary to excess peripheral conversion of estrogens in adipose tissue. Other epidemiologic risk factors include insulin resistance and polycystic ovary syndrome (PCOS).

Medication Factors

More women are taking tamoxifen now than ever before based on data suggesting that tamoxifen may decrease the incidence of breast cancer in women who are at high risk, but do not necessarily have the disease themselves. Although tamoxifen acts as an estrogen antagonist in the breast, it has been associated with various benign and malignant alterations of the endometrium, including EIN.

Screening and Detection

There is no screening test for EIN. Most women will present with symptoms—postmenopausal bleeding (or staining) or intermenstrual or heavy menses in the premenopausal patient. Due to the early onset of symptoms, most women with endometrial cancer will be diagnosed with early stage disease (stage 1). The scenario is different with early serous cancers that might not be associated with bleeding or symptoms. Here the concept of a molecular screening test is valid and under exploration.

Hysteroscopy and Sonography

Endometrial visualization by hysteroscopy or vaginal ultrasonography can be a useful adjunct to biopsy, but practice in this regard is not standardized. Hysteroscopically guided endometrial biopsies have been increasingly performed in clinical settings where practitioners are comfortable with this technology. Hysteroscopically guided resection has also been used for the purpose of fertility preservation. A smooth regular lining by hysteroscopy can reassure the clinician that an occult carcinoma was not missed, and direct visual guidance can improve access to remote regions of an irregularly shaped cavity. Transvaginal ultrasound is an insensitive and nonspecific screen for endometrial cancer, and there are few studies on the ability to detect physically small EIN lesions. Cancer detection sensitivity for transvaginal ultrasound with a threshold endometrial thickness of 6 µm is only 17%, and it is 33% for a threshold value of 5 mm. The specificity is very low, making this an expensive (during follow-up of numerous false-positives) and insensitive test. Ultrasound will, however, identify conformational abnormalities of the uterine cavity that may complicate access for sampling.

Endometrial Sampling

Endometrial biopsy and curettage remain the primary diagnostic modalities to evaluate potential endometrial disease. These are invasive procedures that can cause cramping and bleeding and carry minimal risks of uterine perforation or contamination of the cavity by pathogens. For these reasons, endometrial sampling cannot be considered a screening test but rather a procedure undertaken in response to specific symptoms or cancer risk factors. The most common setting in which an EIN-yielding endometrial biopsy is performed is a workup of menstrual irregularity in a perimenopausal woman or symptomatic bleeding in a postmenopausal patient. Introduction of the Pipelle biopsy apparatus, which unlike curettage does not necessitate cervical dilation and anesthesia, has greatly reduced the cost and morbidity of endometrial sampling. Outpatient, office-based, Pipelle biopsies are now the most commonly performed endometrial sampling procedure.

Sampling Devices

Transcervical endometrial sampling is the mainstay of endometrial diagnosis. Sampling adequacy is of particular concern with localizing EIN lesions that are not uniformly represented in all fragments. Coverage is affected by the device used, guidance by hysteroscopy or ultrasound, operator performance, and uterine anatomy. Short of hysterectomy, no sampling strategy is foolproof. If there is any clinical or pathologic concern that the available sample is inadequate or nonrepresentative, the diagnostic process is incomplete, and resampling should be undertaken. It is incumbent on the pathologist to have a clear understanding of sources of sampling and interpretative errors and how these influence options for follow-up diagnostic procedures and to communicate clearly to the clinician.

Curettage by a rigid sharp device is the most established method but has the drawback of requiring cervical dilation and attendant anesthesia. For lesions whose distribution or site of origin is particularly relevant to management, separate acquisition of endometrial and endocervical curettage fractions (fractional curettage) has traditionally been used; however, currently it is not relied on, and the determination of site of origin (cervix vs. endometrium) is determined by histology, immunohistochemistry, and imaging. In addition, curettage is not without its limitations, sampling less than half of the uterine cavity in about 60% of cases.

The Pipelle biopsy instrument, a 3.2-mm diameter flexible cannula that aspirates a core of tissue of approximately 1.5 to 2 µm ( Fig. 17.3 ) as it sweeps across the endometrial surface is small enough that cervical dilation is unnecessary. Because no anesthesia is needed, it may be used readily in a private office setting and is more comfortable to patients than a sharp curettage. Vabra aspiration biopsy is not recommended, and there is widespread use of the Pipelle instrument in many outpatient contexts.

Fig. 17.3

Macroscopic view of endometrial fragment configuration of a specimen obtained by the Pipelle device.

There are now many studies comparing the endometrial sampling adequacy of Pipelle biopsy to curettage. In aggregate, tissue adequacy and diagnostic accuracy weigh in favor of the Pipelle, with a few notable caveats. Physical mass lesions that impinge on the uterine cavity, such as polyps or uterine leiomyomata, may deflect the flexible Pipelle device and lead to blind spots. Insight regarding these underlying conditions may be gained by ultrasonographic studies or physical examination, and sampling errors may be reduced by the use of a rigid sampling device or hysteroscopic guidance. Overall sensitivity and specificity of an endometrial precancer (atypical hyperplasia) diagnosis is 82% to 100% for Pipelle and 67% to 99.8% for Vabra aspiration. Detection of endometrial carcinoma, generally bulky lesions, is even more sensitive—99.6% for Pipelle and 97.1% for Vabra aspiration.

Hysteroscopic biopsies are the least abundant tissue biopsy format, relying on accurate target selection rather than coverage extent to minimize sampling error. In the case of physically small, grossly inapparent EIN lesions, a larger random sample may be advantageous. Small, often crushed, tissue fragments yielded by tiny jaws of the hysteroscopic biopsy device present a diagnostic challenge to the pathologist. Not only is interpretation usually compromised by artifact, but the background context necessary to recognize a localizing EIN lesion may also be missing or poorly represented. Cauterizing sampling devices should be avoided whenever possible because the low resistance of fluid-filled lumens directs the current specifically to glands, causing severe distortion.

Specimen Adequacy

Tissue fragment size, quality of technical processing, and presence or absence of potentially confounding factors will determine the degree of confidence that an EIN lesion can be recognized or excluded in an individual sample. It is common to receive a rather small specimen from the postmenopausal woman whose endometrium is atrophic or inactive. Most of these will simply be scanty specimens, in which there are no findings suggestive of an EIN or adenocarcinoma. A diagnosis describing what is actually present, annotated by a comment regarding abundance, is usually sufficient in these cases. A special case is seen when the stated endometrial curettage contains no endometrial tissue at all, but perhaps only material from an endocervical or vaginal source. A specific comment that no endometrial tissue was identified will alert the clinician to a significant sampling problem.

Specific recommendations for dealing with small, subdiagnostic, or hormonally treated lesions are provided later in this chapter. Some inadequate specimens should be followed by resampling. Interpretative problems in a crushed or cauterized hysteroscopic biopsy might be subsequently resolved by Pipelle or curettage sampling, both of which are less artifact-prone and give broader representation of the endometrial compartment. If the area of concern is within a polyp, follow-up curettage may succeed in getting more of the lesion than that obtained with a flexible Pipelle device. Always clearly specify to the clinician those characteristics of a specimen suggestive of, but subdiagnostic for, EIN.



Much as the German pathologist Koch developed a series of postulates that must be fulfilled to prove the pathogenesis of disease scientifically by a specific infectious organism, similar postulates may be formulated for premalignant disease. Here we list criteria to be fulfilled for a clinically relevant and biologically distinctive category of endometrial precancers, all of which have been met in the case of EIN.

Criterion 1: Endometrioid Intraepithelial Neoplasia Differs From Normal Tissues

An EIN is an actual neoplasm, comprising a monoclonal outgrowth of a single transformed cell from a polyclonal source field. These benign expansile clones have only a marginal advantage beyond normal endometrial tissues and, in the absence of additional genetic damage, lack the ability to invade or metastasize. Lesions with microsatellite instability have marker genotypes that differ from normal source tissues.

Criterion 2: Endometrioid Intraepithelial Neoplasia Shares Some But Not All Features With Carcinoma

Cells in the early stages of endometrial carcinogenesis should have some features that distinguish them from normal tissues and whose retention during progression establishes them as the physical progenitors of carcinoma. Both EIN and endometrial carcinoma are conserved—nonrandom inactivation of a particular X chromosome copy and the presence of particular altered microsatellites—between lesions of individual patients. The genetic alteration of specific genes implicated in endometrial carcinogenesis has been shown to be conserved between EIN and carcinomas that occur in individual patients. This is true for inactivation of the PTEN tumor suppressor gene, mutation of the K-ras oncogene, and epigenetic inactivation of the DNA repair gene MLH1 ; 63% of EIN lesions, for example, have lost the ability to express the tumor suppressor protein from the PTEN gene, a phenotype shared with more than 80% of endometrial cancers.

Criterion 3: Endometrioid Intraepithelial Neoplasia Can Be Diagnosed

Diagnostic criteria applicable to a routine pathology practice are presented here. Additionally, there is an objective reference standard for EIN diagnosis in computerized morphometry of H&E-stained slides. Cytologic and architectural characteristics of H&E-stained tissues are measured to calculate a d score, which indicates EIN when lower than a threshold of 1.0.

Criterion 4: Endometrioid Intraepithelial Neoplasia Increases Risk for Carcinoma

Clinical outcome studies using image analysis or subjective pathologists’ impressions of pathologic endometria to identify subsets of women with EIN have correlated this diagnosis with future or concurrent carcinoma. About 26% to 37% of women diagnosed with EIN already have cancer at the time of diagnosis, and the remainder have a 46-fold elevated cancer risk in the ensuing years (see Fig. 17.1 ).

Criterion 5: Genetic and Hormonal Mechanisms of Carcinogenesis Converge in Endometrioid Intraepithelial Neoplasia

Endometrial expression of the tumor suppressor gene PTEN normally increases in an estrogenic environment. This functional requirement for increased tumor suppression activity of PTEN under estrogen-rich conditions cannot be met in PTEN -defective EIN lesions. Thus, most EIN lesions (those 63% with without PTEN function) will have a defective tumor suppressor response to estrogens. Correspondingly, if the mitogenic effects of estrogens are mitigated by progestins, PTEN mutant endometrial glands undergo selective involution relative to PTEN -intact glands.

Criterion 6: Introducing Endometrioid Intraepithelial Neoplasia Genotype Into an Animal Produces Premalignant Lesions and Heightened Cancer Risk

Some 63% of EIN lesions comprise cells that are defective in the production of the PTEN tumor suppressor gene product. Heterozygote PTEN mutant mice uniformly (100%) develop endometrial hyperplasia, and 21% of these progress to carcinoma.

Biomarkers—PTEN and PAX2

Anti-PTEN antibodies were the first commercially available special stain for neoplastic endometrioid (type I) endometrial disease. Paraffin tissue immunohistochemistry with anti-PTEN antibody 6H2.1 has shown that more than half of endometrioid endometrial adenocarcinomas and their precursor EIN lesions have lost PTEN protein because of genomic mutational or deletional inactivation. Many commercial anti-PTEN antibodies do not work on paraffin-embedded tissues. A working protocol for the successful use of antibody 6H2.1 is available online at . The most common problems are inadequate antigen retrieval, failure to incubate the primary antibody overnight at 4°C (39°F), an antibody titration that is too low (use 1: 00 for older blocks), use of old sections (must be cut and used within a few days), lack of adequate controls to recognize when it is working, and use of dark obscuring counterstains.

Caution is advised when using PTEN immunohistochemistry to make diagnoses of individual patients. It is an insensitive (half of EIN lesions have normal PTEN expression) and nonspecific (more than one-third of normal proliferative and anovulatory endometria contain PTEN-null glands) marker for EIN. PTEN expression is greatly affected by the endocrine and clinical context in which it is applied. Normal endometrial PTEN expression is greatly reduced or lost in secretory and atrophic glands. The absence of expression in these circumstances cannot be equated with loss of function. Correspondingly, an estrogenic environment increases endometrial stromal and normal gland PTEN expression, improving contrast with a localizing PTEN mutant clone.

PTEN or PAX2 immunohistochemistry can, however, be a useful educational tool for pathologists to delineate the extent and configuration of mutant clones and relate these features to routinely stained slides. Fig. 17.4 shows an H&E-stained EIN lesion with matching PTEN immunohistochemistry images to delimit clonal precancerous lesions with single-cell resolution. This educational objective can be segregated from the diagnostic process by setting aside interesting cases and undertaking a batch staining after they have already been signed out. This provides the benefit of comparison of multiple examples without compromising patient care. PTEN immunohistochemistry is not a routine or requisite part of EIN diagnosis.

Fig. 17.4

Loss of PTEN function in endometrial intraepithelial neoplasia (EIN). A, A localizing EIN lesion occupying the right half of the large tissue fragment has clonally inactivated the PTEN tumor suppressor gene. B D, Immunohistochemistry with anti-PTEN antibody 6H2.1. Note the higher density and epithelial thickening in the EIN glands (pale, devoid of PTEN signal) compared with background glands.

There are actually quite a few genes whose inactivation in endometrial carcinogenesis occurs during the premalignant phase and may be detected in EIN lesions, but none have diagnostic value at present, and most are inaccessible without specialized facilities. Microsatellite instability caused by epigenetic inactivation of the MLH1 gene accompanies 17% to 23% of sporadic endometrial carcinomas and may be seen in premalignant lesions. Direct DNA analysis is needed for microsatellite instability detection, although MLH1 immunohistochemistry shows a loss of protein in most of these cases. K-ras mutation occurs in 16% to 20% of premalignant endometrial lesions, but this prevalence is too low to be diagnostically pathognomonic, and its detection requires direct sequencing rather than immunohistochemistry. PAX2 has also been demonstrated to be downregulated in the endometrium, both in latent precancers and EIN. The role of this gene is being studied in endometrial as well as ovarian and tubal carcinogenesis (see Chapters 24 and 25 ). A tumor suppressor commonly inactivated in papillary serous endometrial carcinomas, p53, is only rarely inactivated in endometrioid carcinomas and EIN lesions.

Combined Molecular and Histopathologic Model for Endometrioid Intraepithelial Neoplasia

Latent, premalignant, and malignant phases of EIN-mediated endometrial carcinogenesis are diagrammed in Fig. 17.5 . In one-third of apparently normal women, histologically unremarkable proliferative endometria contain a small fraction of PTEN tumor suppressor gene, mutant, endometrial glands. This phase may be construed as latent because not only do the mutated glands look completely normal under the microscope, but they also progress to EIN and cancer at a very low efficiency. This latent phase may persist for years, with the continued presence of scattered and interspersed mutant glands after many menstrual cycles. Mutant glands are probably represented in the reserve population of cells that regenerate a new functionalis each month. Endocrine factors act on these latent precancers to modulate involution or progression to EIN. Transition to EIN requires accumulation of additional genetic damage in at least one latent precancer cell, which then clonally expands from its point of origin (indicated by expanding arrows) to form a contiguous grouping of tightly packed and cytologically altered glands recognizable as EIN. The monoclonal precancer (EIN) develops internal heterogeneity through mutation and advantageous events selected by local conditions, which result in hierarchical subclones (left to right) of varying success. EIN lesions have only marginal increases in growth potential and retain susceptibility to further growth modulation by hormonal factors. Some involute; others, through additional mutation and selection, reach a stage at which hormonal support is no longer required for survival. Malignant transformation to cancer is defined by the accumulation of sufficient genetic damage to permit invasion of adjacent stromal tissues.

Fig. 17.5

Clonal origin of endometrial intraepithelial neoplasia (EIN). The first genetic changes (e.g., PTEN or PAX2 inactivation) that initiate endometrial carcinogenesis are unaccompanied by any phenotypic alterations at the light microscopic level. This latent phase of a cytologically and architecturally normal but genetically altered cell may persist for years in a normally menstruating woman. Low cancer risk, combined with the lack of a rational therapeutic response, is why systematic screening and treatment of these latent-phase lesions are unwarranted at present. As additional genetic damage accumulates, higher risk, morphologically altered mutant clones declare themselves by demonstrating those architectural and cytologic alterations that distinguish EIN. Malignant transformation of EIN lesions, which occurs at least 46 times more frequently than non-EIN tissues (see Fig. 17.1 ), warrants careful diagnosis and treatment. Endocrine modifiers of endometrial cancer risk act on the latent and EIN phases of this sequence by tipping the balance of clonal expansion versus involution.

A framework for EIN diagnosis is shown in Table 17.1 . Notable is the clear separation of endometrial changes caused by unopposed estrogens from carcinoma and EIN.


The distribution of a lesion is useful in distinguishing among the diffuse field-wide effects of an abnormal hormonal environment (anovulation, or persistent estrogen effect), surface changes secondary to stromal breakdown, and more focal EIN ( Fig. 17.6 ). Clonal origin from a single cell requires EIN lesions to begin as local processes within the endometrial compartment. Early EIN lesions are easily diagnosed by their contrast in architecture and cytology with the background from which they have emerged. Over time, EIN lesions may completely overrun the background endometrium, thereby removing that convenient lesion to background contrast in morphology, which assists in EIN diagnosis. For this reason, or because of fragmentation, many EIN lesions must be diagnosed without the benefit of comparison with companion benign tissues. Exclusion of artifact and careful evaluation of the architectural and cytologic features of EIN usually permit accurate diagnosis in these cases.

Fig. 17.6

Schematic topography of endometrial intraepithelial neoplasia (EIN). Benign, premalignant, and malignant endometrial processes have differing large-scale architectures and distribution within the endometrial compartment. Reparative or degenerative changes lead to epithelial piling up and loss of polarity in regions of stromal breakdown or offending stimulus. Benign systemic effects (e.g., unopposed estrogens) tend to induce changes throughout the endometrial field, with responsive individual glands randomly scattered throughout. In contrast, EIN lesions begin at a single point in space, growing outward as a compact mass of individual glands with altered cytology. Initially, they have the appearance of a physical patch or geographic domain composed of glands with altered cytology and architecture, eventually overtaking the entire endometrial compartment. Malignant transformation is accompanied by loss of the single-layered individual glands of EIN. The epithelium may become stratified, cribriform, or solid and arranges itself in folded sheets or complex villoglandular structures. Myoinvasion is rarely seen in biopsies, because of sampling limitations.

Diagnostic Criteria

All the diagnostic criteria of Table 17.2 , and presented in the following discussion, must be met to make an EIN diagnosis. The entire slide should first be scrutinized under low magnification for localizing lesions and, if found, these areas should be examined under higher power to assess possible changes in cytology within the architecturally distinct focus. Widespread EIN lesions that have replaced the entire endometrial compartment tend to have a sufficiently atypical cytology that background normal endometrium is no longer required as a reference point for accurate diagnosis.

Table 17.2

Endometrial Intraepithelial Neoplasia (EIN) Diagnostic Criteria

EIN Criterion Comments
Architecture Area of glands > stroma
Cytology Cytology differs between architecturally crowded focus and background or clearly abnormal
Size > 1 mm Maximum linear dimension exceeds 1 mm
Exclude mimics Benign conditions with overlapping criteria (e.g., basalis, secretory, polyps, repair)
Exclude cancer Carcinoma if mazelike glands, solid areas, polygonal mosaic-like glands, myoinvasion, or significant cribriforming

Modified from Silverberg SG, Mutter GL, Kurman RJ, et al: Tumors of the uterine corpus: epithelial tumors and related lesions. In Tavassoli FA, Stratton MR, editors: WHO classification of tumors: pathology and genetics of tumors of the breast and female genital organs. Lyon, France, 2003, IARC Press, pp 221–232.

Size, architecture, and cytology features are easy EIN diagnostic criteria. Much more difficult are the exclusion of benign mimics and adenocarcinoma from the differential diagnosis. There are no simple rules for benign mimic exclusion. The broad universe of competing entities can only be recognized on sight by one who has the easy familiarity that comes with experience. Consistent demarcation of the EIN–adenocarcinoma threshold remains important clinically because it provides a basis for the clinician to evaluate the risks of electing hormonal rather than surgical therapy for younger patients who wish to retain fertility.

Special diagnostic challenges, such as recognition of EIN within polyps, interpretation of subdiagnostically small or fragmented lesions, and interpretation of lesions with nonendometrioid differentiation, have specific caveats that should be carefully studied (discussed later).


The gland area exceeds the stromal area. A cardinal architectural feature of endometrial precancers is glandular crowding, with a threshold quantitative cutoff for EIN lesions of less than half the tissue area occupied by stroma (volume percentage stroma [VPS]). Areas with large dominant cysts should always be avoided when making this assessment. Although EIN is an epithelial disease, visual assessment of the glands themselves is complicated by frequent artifactual displacement from associated stroma, pale staining of most epithelia, and visual shimmering between gland epithelia and lumens. These may all be avoided by focusing on the stromal compartment, which has the significant advantages of a more uniform composition throughout the specimen and superior staining qualities. By focusing on the stroma itself, only intact fragments in which stroma has not been avulsed from glands will be evaluated.

Careful review of graphic ( Fig. 17.7 ) and histologic examples of varying stromal densities will assist in training your eye to classify patient material as above or below the diagnostic threshold. EIN lesions tend to cluster, with a median VPS of about 40%, and non-EIN (benign) lesions cluster at a median VPS of approximately 75%. These differences are sufficiently great that visual assessment by a trained eye can be informative.

Fig. 17.7

Gland crowding (volume percentage stroma [VPS]) correlates with clonal precancers and clinical cancer outcome. Shown is the correlation of architectural feature of VPS with molecular benchmarks of premalignant disease (monoclonal growth; red symbols, left scattergram ) and clinical cancer outcome ( red symbols, right scattergram ). Note the threshold of 55% for both, approximately where the area of glands is that of stroma (VPS, 55%). Tiles on the right show the stromal compartment in dark blue for a range of gland-packing densities.


The cytology of an architecturally crowded area is different from background or clearly abnormal. There is no absolute standard for cytologic features of EIN lesions, but the cytology of EIN is usually clearly demarcated as divergent from that of coexisting benign endometrial tissues in the same patient ( Fig. 17.8 ). The manner of cytologic change in EIN varies considerably from patient to patient and can include, but is not be limited to, increased variation in nuclear size and contour, clumped or granular chromatin texture, change in nucleoli, change in the nuclear-to-cytoplasmic (N/C) ratio, and altered cytoplasmic differentiation ( Fig. 17.9 ). Stereotypical static descriptions of cytologic atypia, such as nuclear rounding and appearance of nucleoli, are met in many but not all EIN lesions. In this sense, a fixed presentation of cytologic atypia is not a prerequisite for EIN. Attempts to define an absolute standard are confounded by the extreme morphologic plasticity of endometrial glandular cells under changing hormonal, repair, and differentiation conditions.

Fig. 17.8

Cytologic demarcation at the endometrial intraepithelial neoplasia (EIN) perimeter. A, B, Two different examples of the perimeter of EIN lesions. Within each panel, EIN glands are to the left; normal background glands are on the right upper left.

Fig. 17.9

A–D, Endometrioid cytology in endometrial intraepithelial neoplasia (EIN). Nuclear cytomorphology can vary greatly among patients.

Cytologic changes in some EIN lesions are manifest as a change in differentiation state to a tubal ( Fig. 17.10 ), mucinous ( Fig. 17.11 ), micropapillary ( Fig. 17.12 ), or eosinophilic ( Fig. 17.13 ) phenotype. These must be distinguished from the scattered random pattern of hormonally or surface-located, repair-induced metaplasias. Further details of how to interpret nonendometrioid EIN lesions are presented later in this chapter.

Fig. 17.10

Endometrial intraepithelial neoplasia (EIN), with tubal differentiation.

Fig. 17.11

Endometrial intraepithelial neoplasia (EIN), with mucinous differentiation.

Fig. 17.12

Endometrial intraepithelial neoplasia (EIN), with micropapillary differentiation. This lesion evolved into a type I (endometrioid class) adenocarcinoma, shown by conservation of genetic changes between this EIN and subsequent carcinoma.

Fig. 17.13

A , B, Endometrial intraepithelial neoplasia (EIN), with eosinophilic differentiation. Both lesions were followed by progression to a well-differentiated endometrioid carcinoma.

In patients in whom there are no normal glands for internal reference, it is necessary to assess the free-standing cytology of relevant fragments in the context of their architectural features. Some EIN lesions occupy the entire tissue sample and should not be underdiagnosed for lack of a convenient benign gland in the area.


An EIN lesion is larger than 1 µm in maximum dimension. Accurate EIN diagnosis requires a contiguous field of glands sufficiently large to enable reliable assessment of architecture. A minimum lesion size of 1-µm maximum dimension was required in previous clinical outcome studies for an EIN lesion to be designated as an elevated cancer risk. The area of an EIN lesion that meets architectural (gland area) and cytologic (changed) criteria for diagnosis must measure at least 1 µm in maximum dimension, a scale that usually encompasses more than 5 to 10 glands ( Fig. 17.14 ). Most biopsy formats produce tissue fragments in excess of 1.5 to 2 mm. The size requirement must be met in a single tissue fragment, not added among multiple fragments. There is no formal evidence that once beyond the minimum 1 mm, EIN lesions should be stratified by size, but if a lesion is discretely focal, it may be of interest to the clinician to know what fraction of the available curettings contains a lesion.

Feb 26, 2019 | Posted by in GYNECOLOGY | Comments Off on Preinvasive Endometrial Neoplasia

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