Introduction

In 2008, an estimated 530,000 women had a diagnosis of cervical cancer and 275,000 women died from the disease, corresponding to age-standardised incidence and mortality rates (ASIR and ASMR) of 15 and 8 per 100,000 women, respectively. Globally, it was the third most common cancer after breast cancer; however, in developing countries, where over 80% of cases are diagnosed, it was the most common cancer in women. It was the fourth most common cause of death ranking below breast cancer (458,000 deaths), lung cancer (427,000 deaths), and colorectal cancer (288,000 deaths). A striking variation of incidence of cervical cancer was reported in different regions of the world. For instance, the lowest burden occurred in Australia and New Zealand (ASIR of 5.0 per 100,000 women and ASMR of 1.4 per 100,000 women) compared with Eastern Africa (ASIR of 34.5 per 100,000 women and ASMR of 25.3 per 100,000 women). Cervical cancer was the most common cancer cause of death in women in Eastern Africa, South-Eastern Asia and Melanesia. Historically, the incidence and mortality rates from cervical cancer correlate relatively well with the existence of cervical cancer prevention programmes, largely cytology based.

History of cytology of the cervix and vagina

Cervical cytology testing involves collecting exfoliated cells from the cervix and examining these cells microscopically. The concept of using exfoliated cells to identify women with invasive cervical cancer was introduced by Papanicolaou and Babes in the 1920s. Subsequently, Papanicolaou refined his technique, and in 1941 published on the use of conventional cytology to identify invasive cervical cancers. In 1954, he published on how to identify and classify cervical cancer precursors. In the first paragraph of the 1941 article, the authors state:

‘The death rate from carcinoma of the female genital tract is approximately 32,000 per year in the United States and of this figure, four-fifths or 26,000 deaths may be said to be due to cancer of the uterus. This rate has remained practically constant during the past twenty five years.’

What is interesting is that, in 2011, the situation in many developing countries is not so different from that in the USA more than 70 years ago. Even in 1941, it was noted that early diagnosis and treatment yielded ‘a high percentage of cures in both carcinoma of the fundus and of the cervix.’ It was not, however, until the 1960s that cervical cytology began to be used widely in many developed countries as a tool for cervical cancer prevention.

Papanicolaou separated cervical cytology findings into five categories (classes I–V), and focused on how closely the cells resembled truly malignant cells ( Table 1 ).

It has long been recognised that cervical cancer develops from histologically well-characterised precursors. The first evidence suggesting the existence of precursor lesions for invasive squamous carcinoma of the cervix were observations made in the late 1800s that non-invasive epithelial abnormalities frequently existed adjacent to invasive lesions. Schottlander and Kermauner were quoted in Wright and Kurman as being the first to propose the term carcinoma in-situ (CIS) to describe these intraepithelial abnormalities.

Subsequently, a number of case-controlled studies showed that a significant proportion of women with CIS, who were untreated, developed cervical cancer. Petersen followed 127 women with biopsy-confirmed, high-grade preinvasive lesions of the cervix (epithelial hyperplasia with nuclear abnormalities) for a minimum of 3 years. He found that overt cervical cancer developed in 4% of women at the end of 1 year, 11% at the end of 3 years, 22% at the end of 5 years and in 33% at the end of 9 years of follow up. Kottmeier found that 25 out of 34 women with CIS who were followed for 20 years or more without treatment developed invasive cancer.

In a study by Koss et al., lesions of women with CIS were confirmed histologically by biopsy and then followed using cytology alone. Four out of 67 women (6%) developed invasive cancer between 16 and 54 months after entering the study and five out of 67 (7%) women developed possible invasion. Hall and Walton reported a 29% progression rate of severe dysplasia to carcinoma in situ or invasive cancer over a 1–14 year period.

In the 1950s, it became apparent that another large group of cervical lesions had some of the characteristics of CIS, but to a lesser degree. Reagan et al. first introduced the term dysplasia to describe these lesions. Dysplasia referred to abnormalities that included a cytological and histological spectrum of lesions intermediate between CIS and normal epithelium. The World Health Organization introduced this terminology as ‘mild, moderate, severe dysplasia’ and CIS for ‘cytological and histopathological classification of cervical cancer precursors’.

The natural history of dysplasia was studied extensively in the 1950s and 1960s. Population-based screening programmes of previously unscreened populations showed that women with mild dysplasia were younger than women with moderate dysplasia, who in turn were younger than women with severe dysplasia and CIS. This age distribution suggested that mild dysplasia progressed over years to higher grades of dysplasia and finally to CIS. CIS was considered high risk for progression to invasive cancer and was aggressively treated with cone biopsy or hysterectomy.

In the 1960s, Richart introduced a classification for cervical intraepithelial neoplasia (CIN). Laboratory-based studies showed that the differences between the different grades of dysplasia were quantitative as well as qualitative. On the basis of these studies and long-term clinical follow-up studies, Richart suggested that dysplasia and CIS constituted a histological continuum rather than a series of discrete entities and introduced the term ‘cervical intraepithelial neoplasia’. In the original CIN terminology, CIN1 corresponded to mild dysplasia, CIN 2 to moderate dysplasia and CIN3 to severe dysplasia and CIS.

The concept of CIN was strongly influenced by the results of a long-term prospective follow-up study of 557 women who had had three previous dysplastic smears. After study entry, the women were prospectively followed for an average of 36 months using cytology and colposcopy without cervical biopsy. During follow up, only 6% of the lesions spontaneously regressed and the remainder either persisted or progressed to higher grades of dysplasia or cancer.

In an attempt to standardise cytology nomenclature, a new classification of cytological reporting, called the Bethesda system, was devised in 1988. The Bethesda system combined clinically similar intraepithelial diagnoses into broad categories, specifically low-grade squamous intraepithelial lesions (LSIL), representing the changes of koiliocytic cytological atypia and CIN1, and high-grade SIL (HSIL), representing the changes of CIN 2 and 3. The Bethesda system of cytological reporting was subsequently revised in 2001 and again in 2006 (for full classification go to www.asccp.org/consensusguidelines ).

LSIL is common and represents the usually benign cytopathological signs of human papilloma virus (HPV) infection. In contrast, HSIL is rare and represents a truly premalignant condition. Although LSIL can be viewed as an epidemiological exposure or risk factor for cervical cancer, HSIL can be viewed as more closely linked to cancer outcome.

Although this conceptual distinction is clinically useful, it is not perfect. A continuum of changes exists that encompass LSIL and HSIL without a clear end point. At a microscopic level, for example, the characteristic cells of LSIL are abnormal but terminally differentiated. The atypical cells progress to the surface, produce keratins, die and exfoliate as would normal cells. The gradient from LSIL to HSIL is characterised by increasing nuclear atypia and failure of cellular differentiation in progressively more superficial levels of epithelium, with CIN3 representing full-thickness replacement of the epithelium with undifferentiated, atypical cells.

History of cytology of the cervix and vagina

Cervical cytology testing involves collecting exfoliated cells from the cervix and examining these cells microscopically. The concept of using exfoliated cells to identify women with invasive cervical cancer was introduced by Papanicolaou and Babes in the 1920s. Subsequently, Papanicolaou refined his technique, and in 1941 published on the use of conventional cytology to identify invasive cervical cancers. In 1954, he published on how to identify and classify cervical cancer precursors. In the first paragraph of the 1941 article, the authors state:

‘The death rate from carcinoma of the female genital tract is approximately 32,000 per year in the United States and of this figure, four-fifths or 26,000 deaths may be said to be due to cancer of the uterus. This rate has remained practically constant during the past twenty five years.’

What is interesting is that, in 2011, the situation in many developing countries is not so different from that in the USA more than 70 years ago. Even in 1941, it was noted that early diagnosis and treatment yielded ‘a high percentage of cures in both carcinoma of the fundus and of the cervix.’ It was not, however, until the 1960s that cervical cytology began to be used widely in many developed countries as a tool for cervical cancer prevention.

Papanicolaou separated cervical cytology findings into five categories (classes I–V), and focused on how closely the cells resembled truly malignant cells ( Table 1 ).

It has long been recognised that cervical cancer develops from histologically well-characterised precursors. The first evidence suggesting the existence of precursor lesions for invasive squamous carcinoma of the cervix were observations made in the late 1800s that non-invasive epithelial abnormalities frequently existed adjacent to invasive lesions. Schottlander and Kermauner were quoted in Wright and Kurman as being the first to propose the term carcinoma in-situ (CIS) to describe these intraepithelial abnormalities.

Subsequently, a number of case-controlled studies showed that a significant proportion of women with CIS, who were untreated, developed cervical cancer. Petersen followed 127 women with biopsy-confirmed, high-grade preinvasive lesions of the cervix (epithelial hyperplasia with nuclear abnormalities) for a minimum of 3 years. He found that overt cervical cancer developed in 4% of women at the end of 1 year, 11% at the end of 3 years, 22% at the end of 5 years and in 33% at the end of 9 years of follow up. Kottmeier found that 25 out of 34 women with CIS who were followed for 20 years or more without treatment developed invasive cancer.

In a study by Koss et al., lesions of women with CIS were confirmed histologically by biopsy and then followed using cytology alone. Four out of 67 women (6%) developed invasive cancer between 16 and 54 months after entering the study and five out of 67 (7%) women developed possible invasion. Hall and Walton reported a 29% progression rate of severe dysplasia to carcinoma in situ or invasive cancer over a 1–14 year period.

In the 1950s, it became apparent that another large group of cervical lesions had some of the characteristics of CIS, but to a lesser degree. Reagan et al. first introduced the term dysplasia to describe these lesions. Dysplasia referred to abnormalities that included a cytological and histological spectrum of lesions intermediate between CIS and normal epithelium. The World Health Organization introduced this terminology as ‘mild, moderate, severe dysplasia’ and CIS for ‘cytological and histopathological classification of cervical cancer precursors’.

The natural history of dysplasia was studied extensively in the 1950s and 1960s. Population-based screening programmes of previously unscreened populations showed that women with mild dysplasia were younger than women with moderate dysplasia, who in turn were younger than women with severe dysplasia and CIS. This age distribution suggested that mild dysplasia progressed over years to higher grades of dysplasia and finally to CIS. CIS was considered high risk for progression to invasive cancer and was aggressively treated with cone biopsy or hysterectomy.

In the 1960s, Richart introduced a classification for cervical intraepithelial neoplasia (CIN). Laboratory-based studies showed that the differences between the different grades of dysplasia were quantitative as well as qualitative. On the basis of these studies and long-term clinical follow-up studies, Richart suggested that dysplasia and CIS constituted a histological continuum rather than a series of discrete entities and introduced the term ‘cervical intraepithelial neoplasia’. In the original CIN terminology, CIN1 corresponded to mild dysplasia, CIN 2 to moderate dysplasia and CIN3 to severe dysplasia and CIS.

The concept of CIN was strongly influenced by the results of a long-term prospective follow-up study of 557 women who had had three previous dysplastic smears. After study entry, the women were prospectively followed for an average of 36 months using cytology and colposcopy without cervical biopsy. During follow up, only 6% of the lesions spontaneously regressed and the remainder either persisted or progressed to higher grades of dysplasia or cancer.

In an attempt to standardise cytology nomenclature, a new classification of cytological reporting, called the Bethesda system, was devised in 1988. The Bethesda system combined clinically similar intraepithelial diagnoses into broad categories, specifically low-grade squamous intraepithelial lesions (LSIL), representing the changes of koiliocytic cytological atypia and CIN1, and high-grade SIL (HSIL), representing the changes of CIN 2 and 3. The Bethesda system of cytological reporting was subsequently revised in 2001 and again in 2006 (for full classification go to www.asccp.org/consensusguidelines ).

LSIL is common and represents the usually benign cytopathological signs of human papilloma virus (HPV) infection. In contrast, HSIL is rare and represents a truly premalignant condition. Although LSIL can be viewed as an epidemiological exposure or risk factor for cervical cancer, HSIL can be viewed as more closely linked to cancer outcome.

Although this conceptual distinction is clinically useful, it is not perfect. A continuum of changes exists that encompass LSIL and HSIL without a clear end point. At a microscopic level, for example, the characteristic cells of LSIL are abnormal but terminally differentiated. The atypical cells progress to the surface, produce keratins, die and exfoliate as would normal cells. The gradient from LSIL to HSIL is characterised by increasing nuclear atypia and failure of cellular differentiation in progressively more superficial levels of epithelium, with CIN3 representing full-thickness replacement of the epithelium with undifferentiated, atypical cells.