Cytology, liquid-based cytology and automation

Quality-assured, comprehensive, cytology-based population screening programmes have resulted in a substantial decline in the incidence of, and mortality from, cervical cancer. Cytology classification systems divide squamous cell abnormalities into low grade and high grade. Women with high-grade squamous abnormalities, cytology suggestive of glandular neoplasia, or invasive disease are referred immediately for investigation. Previously, the optimal management of women with low-grade cytology was uncertain. The introduction of liquid-based cytology has improved specimen adequacy and laboratory productivity, and also provided the platform for human papillomavirus testing for triage of low-grade abnormality, follow up after treatment and, ultimately, primary screening with triage to cytology, particularly in HPV-vaccinated populations. Liquid-based cytology is also ideal for automation-assisted reading of cervical cytology samples; however, recent studies have reported that automation-assisted reading is less sensitive than manual reading and does not reduce the risk of cervical cancer.

Principles of cytology

Cytology-based cervical cancer screening programmes were established in many developed countries after the Second World War. This followed on from the initial serendipitous observation of cervical cancer cells from wet fixed vaginal cytology preparations by George Papanicolaou and the subsequent reports that similar cells could be observed in samples taken from apparently normal cervices in healthy women. Quality-assured, cytology-based population screening for cervical cancer precursors has significantly reduced the incidence of, and mortality from, invasive cervical carcinoma. It has been estimated that cytology-based population screening has prevented up to 4500 deaths per annum in England: it is a simple, safe and inexpensive method of detecting cervical pre-malignancy. Provided that the sample is correctly taken and interpreted with skill and care, it will present clinicians with reliable information about the state of the cervix and enable them to reassure patients about their risk of cervical neoplasia with a high degree of confidence.

Worldwide, nearly half a million new cases of cervical carcinoma are diagnosed per annum, of which over three-quarters occur in developing countries, where at best cervical screening is opportunistic and a cervical cytology test is only available on request. By contrast, in many developed countries, screening healthy women for preinvasive and early invasive cancer of the cervix is highly organised and well women are invited at regular intervals to attend for their cytology test. Individual cytology tests, however, are only moderately accurate and do not achieve concurrent high sensitivity and specificity for the detection of precancerous lesions and treatable cancers. Therefore, acceptable programme efficacy is only achieved by repeating the tests at relatively frequent intervals.

In countries with organised screening programmes, such as the UK, Denmark and the Netherlands, the interval between tests is 3 or 5 years. The frequency of screening in these countries is largely determined by the resources available for the screening programme. Where resources are limited, it has been found that screening every fifth year, with a compliance rate of 80%, is a much more effective way of reducing cancer mortality and morbidity than annual or 3-yearly screening of a small proportion of women at risk.

The target population can only be defined in terms of age. Attempts to define ‘at risk’ groups using socio-sexual parameters, such as smoking habits or sexual behaviour, are not supported by the available evidence. In England, a cervical cytology test is offered every 3 years to all women aged between 25 and 49 years, and every 5 years to women aged between 50 and 64 years. Cervical cytology ceases in women with a negative (normal) screening history at the age of 65 years. This policy, introduced in 2004, is predicted to prevent 63% of cervical cancers in women aged 20–79 years compared with an unscreened population. Further reductions in the incidence of cervical cancer could be achieved by increasing the sensitivity of the screening test (see below) or extending screening to older women. In contrast to previous practice, there is no justification for taking a second cytology test 1 year after the first negative test, or additional tests in the following circumstances: when a women is starting oral contraceptive treatment; having an intrauterine contraceptive device inserted; is pregnant; has genital warts or herpes; or admits to being a heavy smoker, provided that the women is asymptomatic, is participating in the routine screening programme and has had a negative test within the previous 3 or 5 years. Women who are HIV positive, however, should be screened annually as they are recognised to have a higher incidence of cervical neoplasia.

Classification systems for cytology

All the cytology classification systems used worldwide essentially divide samples containing abnormal squamous cells into two groups: conceptually these are thought of as low grade and high grade to reflect clinical management strategies. Low-grade squamous abnormalities are usually associated with only human papillomavirus (HPV)-related lesions, cervical intraepithelial neoplasia (CIN) 1, or both. High-grade squamous abnormalities are usually associated with CIN 2 or worse histological abnormality. Low-grade squamous abnormalities may be managed by either surveillance (only referred for colposcopy if the abnormality persists) or referral for colposcopy. High-grade squamous abnormalities are an indication for immediate referral for colposcopy. Specific categories also exist for defining inadequate or unsatisfactory samples; cytological abnormalities in which it is uncertain whether they are the result of inflammation or neoplasia; the possibility of invasive squamous carcinoma; and glandular neoplasia of the cervix and elsewhere in the female genital tract.

The following international cervical cytology test systems are presented in Table 1 : the British Society for Clinical Cytology (BSCC) terminology used to report cervical cytology tests in the UK; a proposed new BSCC terminology; the more widely used Bethesda system, developed in the USA; and terminology used in Europe and Australia. The Bethesda and Australian systems differ from the current BSCC system because they use a two-tier rather than a three-tier grading system for reporting neoplastic changes in squamous cells: high-grade squamous intraepithelial lesion and low-grade squamous intraepithelial lesion. They also report atypical squamous cells of undetermined significance or atypical glandular cells of undetermined significance, corresponding to borderline change in the BSCC system. In the Bethesda system all specimens showing koilocytosis, the cytopathological hallmark of human HPV infection, are reported as low-grade squamous intraepithelial lesion, whereas in the UK koilocytes showing only slight nuclear atypia owing to HPV infection are considered to show borderline changes. It is likely that, in the near future, the UK cervical screening programmes will also use the BSCC terminology, and thereby a two-tier system of low-grade and high-grade dyskaryosis; however, it will still be possible to distinguish between moderate and severe dyskaryosis within high-grade dyskaryosis to guide clinical management, particularly in young women.

Table 1
Comparison of commonly used cervical cytology terminology systems.
BSCC 1986 Proposed new BSCC terminology The Bethesda system 2001 ECTP AMBS 2004
Negative Negative Negative for intraepithelial lesion or malignancy Within normal limits Negative
Inadequate Inadequate Unsatisfactory for evaluation Unsatisfactory due to… Unsatisfactory
Borderline nuclear change Borderline change, squamous, but not otherwise specified Borderline change, high-grade dyskaryosis not excluded Borderline change in endocervical cells Atypical squamous cells of undetermined significance Atypical squamous cells (cannot exclude high-grade squamous intra-epithelial lesions) Atypical endocervical/ endometrial/glandular cells: not otherwise specified or favour neoplastic Koilocytes (without changes suggestive of intraepithelial neoplasia) Squamous cell changes (not definitely neoplastic but merit early repeat) Possible low-grade squamous intraepithelial lesion Possible high-grade squamous intraepithelial lesion
Mild dyskaryosis Low-grade dyskaryosis (includes all cases of koilocytosis provided that no high-grade dyskaryosis is present) Low-grade squamous intraepithelial lesion Mild dysplasia (CIN 1) Low-grade squamous intraepithelial lesion
Moderate dyskaryosis High-grade dyskaryosis High-grade squamous intraepithelial lesion Moderate dysplasia (CIN 2) High-grade squamous intraepithelial lesion
Severe dyskaryosis Severe dysplasia (CIN 3) Carcinoma in situ (CIN 3)
Severe dyskaryosis/? invasive Severe dyskaryosis/? Invasive Squamous cell carcinoma Severe dysplasia ?invasive Invasive squamous cell carcinoma Squamous cell carcinoma
? Glandular neoplasia ? Glandular neoplasia Endocervical Non-cervical 1. Endocervical carcinoma in situ 2. Adenocarcinoma Endocervical Endometrial Extrauterine Not otherwise specified Adenocarcinoma Adenocarcinoma in situ Endocervical Endometrial Extrauterine Not otherwise specified Endocervical adenocarcinoma in situ Adenocarcinoma
AMBS, Australian Modified Bethesda System ; BSCC, British Society for Clinical Cytology; CIN, cervical intraepithelial neoplasia; ECTP, European Commission Training Programme.

Classification systems for cytology

All the cytology classification systems used worldwide essentially divide samples containing abnormal squamous cells into two groups: conceptually these are thought of as low grade and high grade to reflect clinical management strategies. Low-grade squamous abnormalities are usually associated with only human papillomavirus (HPV)-related lesions, cervical intraepithelial neoplasia (CIN) 1, or both. High-grade squamous abnormalities are usually associated with CIN 2 or worse histological abnormality. Low-grade squamous abnormalities may be managed by either surveillance (only referred for colposcopy if the abnormality persists) or referral for colposcopy. High-grade squamous abnormalities are an indication for immediate referral for colposcopy. Specific categories also exist for defining inadequate or unsatisfactory samples; cytological abnormalities in which it is uncertain whether they are the result of inflammation or neoplasia; the possibility of invasive squamous carcinoma; and glandular neoplasia of the cervix and elsewhere in the female genital tract.

The following international cervical cytology test systems are presented in Table 1 : the British Society for Clinical Cytology (BSCC) terminology used to report cervical cytology tests in the UK; a proposed new BSCC terminology; the more widely used Bethesda system, developed in the USA; and terminology used in Europe and Australia. The Bethesda and Australian systems differ from the current BSCC system because they use a two-tier rather than a three-tier grading system for reporting neoplastic changes in squamous cells: high-grade squamous intraepithelial lesion and low-grade squamous intraepithelial lesion. They also report atypical squamous cells of undetermined significance or atypical glandular cells of undetermined significance, corresponding to borderline change in the BSCC system. In the Bethesda system all specimens showing koilocytosis, the cytopathological hallmark of human HPV infection, are reported as low-grade squamous intraepithelial lesion, whereas in the UK koilocytes showing only slight nuclear atypia owing to HPV infection are considered to show borderline changes. It is likely that, in the near future, the UK cervical screening programmes will also use the BSCC terminology, and thereby a two-tier system of low-grade and high-grade dyskaryosis; however, it will still be possible to distinguish between moderate and severe dyskaryosis within high-grade dyskaryosis to guide clinical management, particularly in young women.

Table 1
Comparison of commonly used cervical cytology terminology systems.
BSCC 1986 Proposed new BSCC terminology The Bethesda system 2001 ECTP AMBS 2004
Negative Negative Negative for intraepithelial lesion or malignancy Within normal limits Negative
Inadequate Inadequate Unsatisfactory for evaluation Unsatisfactory due to… Unsatisfactory
Borderline nuclear change Borderline change, squamous, but not otherwise specified Borderline change, high-grade dyskaryosis not excluded Borderline change in endocervical cells Atypical squamous cells of undetermined significance Atypical squamous cells (cannot exclude high-grade squamous intra-epithelial lesions) Atypical endocervical/ endometrial/glandular cells: not otherwise specified or favour neoplastic Koilocytes (without changes suggestive of intraepithelial neoplasia) Squamous cell changes (not definitely neoplastic but merit early repeat) Possible low-grade squamous intraepithelial lesion Possible high-grade squamous intraepithelial lesion
Mild dyskaryosis Low-grade dyskaryosis (includes all cases of koilocytosis provided that no high-grade dyskaryosis is present) Low-grade squamous intraepithelial lesion Mild dysplasia (CIN 1) Low-grade squamous intraepithelial lesion
Moderate dyskaryosis High-grade dyskaryosis High-grade squamous intraepithelial lesion Moderate dysplasia (CIN 2) High-grade squamous intraepithelial lesion
Severe dyskaryosis Severe dysplasia (CIN 3) Carcinoma in situ (CIN 3)
Severe dyskaryosis/? invasive Severe dyskaryosis/? Invasive Squamous cell carcinoma Severe dysplasia ?invasive Invasive squamous cell carcinoma Squamous cell carcinoma
? Glandular neoplasia ? Glandular neoplasia Endocervical Non-cervical 1. Endocervical carcinoma in situ 2. Adenocarcinoma Endocervical Endometrial Extrauterine Not otherwise specified Adenocarcinoma Adenocarcinoma in situ Endocervical Endometrial Extrauterine Not otherwise specified Endocervical adenocarcinoma in situ Adenocarcinoma
AMBS, Australian Modified Bethesda System ; BSCC, British Society for Clinical Cytology; CIN, cervical intraepithelial neoplasia; ECTP, European Commission Training Programme.

Interpretation of the cervical cytology test report

The inadequate (unsatisfactory) cervical cytology test

Conventional cervical smears may be reported as inadequate for a number of reasons: (1) the degree of cellularity is judged to be insufficient, taking account of the woman’s age and hormonal status; (2) it is composed entirely of superficial squamous cells, suggesting that the vagina rather than the cervix has been sampled; (3) it is poorly fixed or air dried; (4) the cellular material is so thickly spread that the epithelial cells cannot be evaluated; (5) the epithelial cells are obscured by blood, menstrual debris, inflammatory cells, bacteria or spermatozoa and cannot be evaluated; (6) it is entirely composed of endocervical cells, unless the only purpose of the test was to sample the endocervical mucosa.

Liquid-based cytology samples are inadequate if insufficient numbers of squamous epithelial cells are present, although robust data on which to base this assessment are limited and further studies are in progress.

Both types of cervical cytology test are reported as inadequate if endocervical cells are not identified in a test taken for follow up of an endocervical glandular abnormality.

Negative

Most cytology tests are reported as negative, indicating that abnormal cells have not been identified. Other information about the specimen, however, that may be useful for the clinician in the management of the patient may be reported, including, for example, information about specific infection, such as trichomonas or candida, or the presence of benign endometrial cells in a specimen from a postmenopausal woman or a woman aged over 40 years.

Squamous neoplasia

Cytology tests containing squamous cells that show varying degrees of nuclear abnormality characterised by abnormal size, spacing, distribution and staining of nuclear chromatin, coupled with irregularity of nuclear outline, indicate the presence of CIN. The grade of abnormality is determined either from the nuclear-cytoplasmic ratio, which is assessed by comparing the area of the nucleus with the area of the affected cell, the nuclear-cytoplasmic diameter ratio, or by comparing the size of intermediate cell nuclei depending on the terminology system used. The most severe degree of abnormality is reported and should always be regarded as indicative of the lowest grade of CIN likely to be present.

Invasive squamous carcinoma

Cytology involves the examination of cells shed from the surface layers of the epithelium covering the cervix and a definitive diagnosis of invasion of the stroma by neoplastic cells cannot be made on the cytology test. Therefore, well-defined cytological features are suggestive of the presence of invasion; however, the cytology report can only provide a provisional diagnosis, and will require confirmation by biopsy.

Glandular neoplasia

Samples with cytological features suggestive of cervical glandular neoplasia or endometrial or extrauterine neoplasia are reported with an appropriate comment regarding the likely site of origin of the tumour.

Borderline nuclear changes

In a small proportion of cases, it is not possible to decide whether the nuclear changes in epithelial cells can be attributed to an inflammatory response or to neoplasia. In such cases, a report of ‘borderline changes’ is given in UK terminology (‘atypical cells’ in the Bethesda system). In general, women with borderline changes in squamous cells are kept under cytological surveillance and only referred for colposcopy if the changes persist or increase in severity. Women with borderline changes in endocervical cells, however, are referred immediately for colposcopy because there is evidence from case series that such women have increased rates of malignant and pre-invasive disease.

Management of abnormal cervical cytology

The management of women with specimens showing high-grade abnormality in squamous cells or features suggestive of squamous dyskaryosis is well defined, but the management of women with low-grade and equivocal abnormalities remains controversial. Current guidance from the NHS Cervical Screening Programme (NHSCSP), based on professional consensus and published evidence, is presented in Table 2 .

Table 2
Interpretation and management of cytology test results. a
Cytology report Explanation Action
Inadequate
  • Conventional smears

  • Insufficient epithelial cellular material; specimen composed entirely of superficial squamous cells or endocervical cells; inadequate fixation; epithelial cells largely obscured by blood, menstrual debris, inflammatory cells, bacteria or spermatozoa; or thickly spread cellular material.

  • Liquid-based cytology samples

  • ThinPrep. Less than 5000 squamous cells present

  • SurePath. Less than 10000 squamous cells present.

  • Repeat sample as soon as convenient.

  • Refer for colposcopy after three consecutive inadequate samples.

Negative No atypical, dyskaryotic or malignant cells identified Routine recall.
Borderline changes Sample in which there is doubt whether the nuclear changes are due to inflammation or neoplasia.
  • Repeat sample in 6 months after one test reported as borderline change in squamous cells (equivalent to atypical squamous cells of undetermined significance in the Bethesda system).

  • Refer for colposcopy after three consecutive samples reported as borderline change in squamous cells or three samples reported as borderline change in squamous cells in a 10-year period.

  • Refer for colposcopy after one test reported as borderline change in endocervical cells or borderline changes in squamous cells, high–grade disease cannot be excluded (equivalent to a typical squamous cells cannot exclude high-grade squamous intra-epithelial lesion

  • in the Bethesda system).

Mild dyskaryosis Squamous cellular changes consistent with origin from CIN 1. Ideally, refer for colposcopy, but repeat sample in 6 months acceptable.
Moderate dyskaryosis Squamous cellular changes consistent with origin from CIN 2. Refer for colposcopy.
Severe dyskaryosis Squamous cellular changes consistent with origin from CIN 3. Refer for colposcopy.
Severe dyskaryosis/? invasive carcinoma Squamous cellular changes consistent with origin from CIN 3. but with additional features that suggest the possibility of squamous carcinoma. Urgent referral for colposcopy.
? glandular neoplasia Cellular changes suggestive of neoplasia in the endocervix, endometrium, adnexae or peritoneum. Urgent referral for colposcopy or gynaecological opinion, depending on the predicted site of the lesion (i.e. endocervix or elsewhere).

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Nov 9, 2017 | Posted by in OBSTETRICS | Comments Off on Cytology, liquid-based cytology and automation

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