Testing for cervical cancer using HPV testing in addition to the Pap smear is unlikely to detect cancer cases that wouldn't be found using HPV testing alone. The main goal of cervical screening programs is to detect and treat precancer before cancer develops. Cytology-based screening, known as the Pap test or Pap smear, is used to detect abnormal cells. The Pap test can also find noncancerous conditions, such as infections and inflammation.
Cervical cancer screening guidelines have changed dramatically over the last 15 years, following introduction of testing for the dozen high-risk human papillomavirus HPV types that cause virtually all cervical cancer and its precursors. Despite more research into HPV, and the introduction of preventive HPV vaccines, screening will remain important and comprise many millions of tests annually for decades to come. But improved screening methods have also introduced some confusion, even controversy.
HPV testing is more sensitive than the Pap test for detecting precancer. The HPV test captures the known cancer causing viruses, but there are gynecologists who believe that there may be unknown cancer causing viruses and so continue to do the Pap smear (plus HPV testing). However, reports of rare HPV-negative, Pap-test-positive cancers are motivating continued use of both tests (cotesting) despite increased testing costs.
An HPV test, in which doctors test a cervicovaginal specimen for the presence of the nucleic acids of carcinogenic types of HPV, is more sensitive than the Pap test (a microscopic examination of exfoliated cells) for detection of precancers. Thus, if a single screening method were chosen to complement HPV vaccination, primary HPV testing likely would gradually supplant the Pap test.
The accumulated evidence supports inclusion of HPV testing in screening; thus, the main choice moving forward is between cotesting and primary HPV testing alone. Researchers were searching for realistic performance data to quantify the additional benefit of the Pap test component of cotesting, as the costs of intensive screening of all women using two screening tests are substantial.
The analysis found that HPV testing identified more women subsequently diagnosed with cancer and precancer than the Pap test. HPV testing was statistically significantly more likely to be positive for cancer at any time point, except within 12 months. HPV-negative/ Pap test-positive results preceded only small fractions of cases of precancer (3.5%) and cancer (5.9%); these cancers were more likely to be regional or distant stage than other cases.
Given the rarity of cancers among screened women, the contribution of the Pap test to screening translated to earlier detection of at most five cases per million women per year. Two-thirds (67.9%) of women found to have cancer up to 10 years. The researchers conclude that the added sensitivity of cotesting versus HPV alone for detection of treatable cancer affected extremely few women.
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