Cytological testing involves collection of exfoliated cells from the cervix and microscopic examination of these cells after staining. The concept of utilizing exfoliative cytology to identify women with invasive cervical cancer was introduced by Papanicolaou and Babes in the 1920s (Papanicolaou, 1928; Papanicolaou & Traut, 1941). Subsequently, Papanicolaou refined the technique and demonstrated that conventional cytology could also be used to identify precancerous lesions of the cervix (Papanicolaou, 1954).
The shift in emphasis from using cytology as a way to identify cases of invasive cervical cancer to using it to identify women with high-grade precursor lesions who are at risk for subsequently developing invasive cervical cancer was highly significant, as it meant that cervical cytology could be used to actually prevent the development of cervical cancer rather than simply identify cases at an early stage. In the 1960s, cervical cytology began to be widely used in many developed countries as a technique for cervical cancer prevention. Although the method was introduced over a half century ago, cytology-based screening programmes continue to be the mainstay of cervical cancer prevention.
The terminology developed by Papanicolaou separated cervical cytological findings into five categories or classes (Table 14) (Papanicolaou, 1954). At the time the classification was developed, there was only limited understanding of the relationship between cervical cancer precursor lesions and invasive cancers. Moreover, invasive cervical cancer was common and cervical cytology was initially viewed as a way of detecting early stage, easily treated cancers.
Therefore, the Papanicolaou classification system focused on how closely the exfoliated cells resembled those from an invasive cancer. Although the Papanicolaou classification was modified many times over the years, the problems inherent in this classification remain. For example, although is clear how Class I and Class V translate into known histological entities, Classes II, III or IV correlate less clearly with standard histopathological lesions. For example, should a carcinoma in situ be classified as Class IV and all grades of dysplasia as Class III, or does mild dysplasia correspond to Class II? There was also no consensus as to what other non-neoplastic conditions were combined in Class II.
Such ambiguity in the Papanicolaou classification resulted in its non-uniform use by different cytologists. Modifications of the Papanicolaou classifications are still used in some countries. In the Netherlands, a modified Papanicolaou system (CISOE-A) is used for classification. This redefined and subdivided the Papanicolaou classes in order to make the terminology correlate with histopathological terminology (Hanselaar, 2002).