PAP-test: Possibilities and Limitations

Abstract

Cervical cancer (CC) progresses slowly, and the cytological screening increases the likelihood of early detection of precancerous lesions. Cytology of the cervix is one of the primary methods of effective CC diagnosis, which, thanks to early detection and timely treatment, leads to a stable decrease in morbidity and mortality from invasive CC. The results of many studies have shown that the specificity of the conventional Pap smear test is approximately 80–100%, its sensitivity ranges from 30% to 80%, and the rate of inadequacy of this method is from 5% to 25%. With traditional smear preparation, only a small percentage of collected cells end up on the slide, while abnormal cells may be discarded and not analyzed. When viewing the slide, cells that have dried and clumped together may interfere with the visualization of atypical cells. To overcome these limitations, in 1996, as an alternative to the traditional Pap test, liquid cytology was presented – the technology of preparing slides on which the cells are placed in a single layer. This technology outperformed the conventional Pap test with improved fixation, reduced obscuring factors, and standardized cell transfer. In liquid cytology samples are collected by fully immersing the cytobrush in a vial containing a preservative liquid, whereby the cells are preserved and fixed simultaneously, unlike conventional smears where the sample is applied to a glass slide and fixed separately. Today, two main methods of preparation based on liquid cytology are known: ThinPrep and SurePath. The results of cytology are described according to the Bethesda system. The Bethesda classification is widely accepted because it corresponds to the clinical presentation, reproduces the nature of the lesions, and is therefore treatmentoriented with a desirable follow-up procedure. The indisputable advantage of the Pap test by liquid cytology is the ability to perform both cytological and molecular studies, in particular HPV, in one sample. This capability facilitated the implementation of a two-step strategy when HPV testing is used as a triage test for ASC-US or low-grade squamous intraepithelial lesion cytology, or when cytology is used to triage HPV-positive women.