Cervical Cancer Screening
What is Cancer Screening?
Screening is done to evaluate an asymptomatic population to identify cancer at an earlier stage than it would have been diagnosed in the absence of screening. The expectation is that early diagnosis and treatment lead to a reduction in mortality from the disease and/or a reduction in the severity of the disease. It is a two phase process since those who have a positive screening test must undergo a diagnostic procedure for confirmation. Screening is NOT DIAGNOSTIC.
What is the role of Screening in Cervical Cancer?
The principal screening test for cervical cancer in developed countries is the Pap smear. A cellular specimen from the cervix is fixed and stained on a slide for visual interpretation in which morphologic changes of precancerous cells, cervical intraepithelial neoplasia (CIN), are identified. Conventional Pap smear screening had specificity of 98% but sensitivity of only 51%.
Patients with abnormal Pap smears are referred for colposcopy, in which 3% to 5% acetic acid is applied to the cervix and examined under magnification with a bright light to enhance lesions for biopsy.
Decline in cervical cancer mortality has been dramatic in United States women, declining >70% between 1930 and 1980. Similar declines in the incidence of invasive cervical cancer have been observed as well. Same pattern of declining incidence and mortality has been observed in other countries that have introduced mass screening for cancer of the cervix.
The relatively low incidence rate of invasive cervical cancer in Western countries compared with other cancers, and the long-term downward trend in incidence and mortality is a measure of the success of the Papanicolaou test. In Norway, where participation rates were lowest, mortality remained comparatively unchanged whereas in Iceland, which organized an aggressive screening program that had high rates of participation, the mortality reduction (73%) was greatest among the five countries.
How is Screening for Cervical Cancer done?
Visual Inspection Methods
It was first introduced in 1930s by Schiller using lugol’s Iodine. It is done with 3-5% Acetic Acid or 45% Lugol’s Iodine (a solution of 5 g of iodine and 10 g of potassium iodide in 100 mL distilled water). Either of them is applied, wait for one minute, inspect cervix for lesions and/or colour changes. This test has a poor specificity but useful in low resource settings.
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Dr. Surendra Srinivas Shastri; Prof. of Preventive Oncology from Tata Memorial Hospital, India used this technique for mass screening in India. Study began in 1998, and recruitment completed in 2002. Women aged 35-64 yrs with no prior history of cancer were included, with 20 clusters of average of 7500 women each. There were 75,360 women from 10 clusters in the screening group and 76,178 women from 10 comparable clusters in the control group, making a total of 151,538 cases.
It has been proposed both as a primary screening modality (either as an adjunct to, or instead of, cervical smear testing). Co-testing is recommended (with cytology) in women >30 years every 5 years. It is also as a method to triage Pap smear results that are equivocal or show low-grade abnormalities.
Types of HPV tests (FDA Approved)
- Hybrid Capture 2 (the first test to receive FDA approval, in 2003) — Identifies the presence of 13 high-risk HPV types
- Cervista HPV HR test (approved in 2009) — Identifies the presence of any of 14 high-risk HPV types
- Cobas HPV test — Detects HPV16 and 18 as well as a pooled result for an additional 12 high-risk subtypes
- Aptima mRNA test — Detects 14 high-risk subtypes
- Cervista (16/18) detects only HPV16 and HPV18 high-risk subtypes and is approved only for use in women 30 and over as a follow-up test after a positive HPV screen for the 14 high-risk types
HPV Screening for Cervical Cancer in Rural India
No significant reduction in numbers of advanced cancers or death were observed in the Cytology group or VIA group. In a low resource setting, a single round of HPV testing was associated with significant reduction in numbers of advanced cervical cancers and deaths from cervical cancer.
You can also read: Risk Factors For Cervical Cancer
What are WHO Guidelines for Cervical Cancer Screening?
Method for screening depends on resources of any given country. In resource poor setting, screening with VIA alone and treating is recommended. HPV test alone can be used for screening. If there are enough resources to offer a sequence of tests, then HPV testing followed by VIA is preferred.
If HPV test is done
If it is negative, rescreening is required after a minimum interval of 5 years.
If it is positive, options are-
- VIA - If VIA is negative, rescreening is required after 1 year. But if it is positive, then cryotherapy or LEEP should be done based on eligibility.
- Colposcopy – If it is negative, rescreening should be done after 3 years. But if it is positive, then cryotherapy or LEEP should be done based on eligibility.
If VIA test is done
If it is negative, rescreening should be done after 3-5 years. But if it is positive, then cryotherapy or LEEP should be done based on eligibility.