Posted online July 30, 2012 on www.jco.org.
Results of a large, population-based study support guidelines on cervical cancer screening released earlier this year, which recommend “co-testing” consisting of human papillomavirus (HPV) testing and conventional Papanicolaou (Pap) testing every five years. Remarkably, researchers also determined that a negative HPV test at a single time point provides greater reassurance that a woman would not develop cervical precancer and cervical cancer over a period of 18 years than a one-time normal Pap test. A positive HPV test is more sensitive but less specific for cervical precancer and cancer than a Pap as the HPV test detects more HPV virus that will go away without consequence. Therefore, Pap is better at predicting which women have cervical precancer and cancer on that day than HPV testing.
More than 20,000 women who enrolled in the study underwent initial high-risk HPV DNA testing and Pap testing. The women were then followed with conventional Pap testing for up to 18 years to determine how well each screening strategy predicted long-term risk of cervical cancer.
HPV infection is the obligatory first step on the road to cervical cancer. Most HPV infections clear in one to two years. Only persistent infections (lasting more than a couple of years) with high-risk HPV types are linked to cervical cancer. It takes on average five to ten years for an HPV infection to progress to cervical precancer and on average 20 to 25 years to go from an HPV infection to invasive cancer. High-risk types HPV16 and HPV18 account for approximately 55% and 15% of all cervical cancers, respectively. This study found that, among women with normal Pap test results, HPV16- and HPV-18 positive women were at elevated risk of developing cervical precancer and cancer over an 18-year period compared with women infected with other HPV types.
What This Means for Patients
The study’s results add to the evidence that women over 30 years old who have a normal Pap test result and test negative for HPV can safely go for five years between screenings, as recommended in the current screening guidelines. Women who do not have access to HPV testing should have Pap tests done every three years. More frequent screening is unlikely to pick up more precancers and cancers but very likely to increase harms such as anxiety, unnecessary diagnostic procedures and treatments. Those unnecessary treatments are linked to an increased risk of pre-term delivery. Women should consider these harms if their doctor offers them more frequent screening.
In addition to allowing for a longer time period between screenings, adding HPV testing to the cervical cancer screening strategy increases the odds of detecting precancer in women with normal Pap smears. HPV-positive, Pap-negative women may undergo separate HPV16 and HPV18 testing, if available, to determine which women might benefit from immediate colposcopy.