Cervical Cancer Screening: PAP Test & HPV DNA

About 95-99,7% of cervical cancer cases are caused by the human papillomavirus (HPV). HPV infection is more common in young, sexually active women under 25 years of age. The average duration of HPV infection is 4-20 months because in 2 years in 90% of people HPV infection is eliminated with the help of the immune system. In the remaining 10%, the infection persists, which is associated with a higher risk of developing intraepithelial flat lesions of the cervix.

More than 120 different types of HPV have been identified, and about one-third of them can infect genital epithelial cells. HPV types with high oncogenic risk: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59. Among them, HPV 16 is the most carcinogenic type, which causes 50-60% of cervical cancer And HPV 18, which is involved in the development of cervical cancer in 10-12% of cases.

Cervical cancer screening

The introduction of screening programs in developed countries leads to a significant and permanent reduction in morbidity and mortality. The purpose of screening is to detect preoperative lesions of the cervix.

Pap test (Also called a smear test) is the most commonly used test for cervical cancer screening. The study cells are collected from the cervical transformation zone and analyzed under a microscope. The introduction of HPV testing has further improved the early detection process of cervical cancer.

Babes-Papanicolaou test (Pap test) by liquid cytology

There are no clinically significant differences between the liquid cytology method (LBC) and the conventional cytology method (conventional Pap test) in terms of their specificity and sensitivity. However, the liquid cytology method has several important advantages:

• The frequency of unsatisfactory samples is significantly reduced - at normal cytology - 9%, at LBC - 1,6%;
• If there is blood in the sample, the LBC technique provides better information;
• Infectious microorganisms such as Candida hyphae, Trichomonas vaginalis, Herpes simplex virus, better detected by LBC technique;
• LBC allows for additional testing and HPV genotyping with the same test material.

The PAP test is a very useful screening tool used in the early stages of cervical cancer, but it should always be followed by other tests before making a therapeutic decision. A Pap test effectively identifies patients who need additional tests (e.g., colposcopy) for the clinician to be able to make a therapeutic decision.

Detection and genotyping of high-risk HPV types

HPV screening test detects high risk 14 HPV types: HPV - 16, 18, 31, 45, 51, 52 - types with individual genotypes and other HPV types - from the 2nd or 3rd group of the virus: P1: 33/58; P2: 56/59/66; P3: 35/39/68. The test is based on the determination of HPV DNA by real-time PCR (PCR) research method. Unlike most HPV tests, it allows the genome to replicate regions of the genome that are specific to a particular type of HPV, thus improving the specificity of detection. In addition, by selecting target sequences at the E6 and E7 gene levels, there is no risk of obtaining a false-negative result except in rare cases. Another potential advantage of the test is that enhanced genotyping may lead to a more accurate assessment of the persistence of HPV-specific genotypes in women participating in screening programs and ultimately better stratification of patients according to the degree of risk.

The test is used for both primary cervical cancer screening and liquid cytology after the Pap test, in the latter case the test can be performed within 3 weeks from the date of the PAP liquid cytological sample on the same test material.

How to prepare for the test?

• Do not take the sample during menstruation;
• Do not take the test if you are pregnant, if you have leukemia, 6-8 weeks after giving birth and during a course of radiation therapy;
• Patients should abstain from sexual intercourse and vaginal shower for 48 hours before taking the sample. The use of intravaginal tampons, topical contraceptives, vaginal gels, creams and medications should be avoided.

Research material

• Cells from both exocervical, endocervical, and transition areas (transformation zone) are required for the study (for both screening tests).
• The study material should be taken by a professional.