Results from a recent Canadian clinical trial published in the Journal of the American Medical Association show that human papilloma virus (HPV) testing is more sensitive in screening for the risk of cervical cancer than Pap smears. Some experts say these results could have an effect on current cervical cancer screening guidelines that recommend co-testing—that is, using both HPV tests and Pap smears—to screen for cervical cancer in women ages 30 to 65.
The American Cancer Society (ACS) estimates that there will be more than 13,000 new cases of cervical cancer diagnosed in 2018, and over 4,000 women will die of the disease. Nearly all cases of cervical cancer in the U.S. are caused by HPV. Out of more than 100 different HPV strains, there are 14 that are high-risk for cervical cancer (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, and 68).
While many HPV infections resolve without treatment, infections with high-risk HPV strains that persist over time can cause cervical cancer. A woman with HPV cervical cancer usually does not show symptoms until the cancer is advanced and hard to treat, so regular screening is important.
The two screening tests work in different ways:
- The HPV test detects the genetic material (DNA) of the virus in samples taken from the cervical area. If a woman has a positive HPV screening test, she may have a persistent infection with a high-risk strain of HPV. She will typically be monitored more closely with repeat testing and may have additional procedures, such as colposcopy and treatment (e.g., surgical removal of abnormal cells or cryotherapy—freezing abnormal cells or tissues.) For additional details, see the article on HPV Test.
- A Pap smear (also known as Pap test or cervical cytology) is a visual, microscopic examination of cells from the cervical area that looks for abnormal or potentially abnormal cells. A woman with an abnormal Pap smear screening result typically has additional testing and may have colposcopy as well as treatment of any abnormal cervical areas. (Read the Pap Test article for additional details.)
Most major health organizations currently recommend co-testing with HPV tests and Pap smears every five years for women ages 30 to 65. For women ages 21 to 29, only the Pap smear is recommended every three years, as HPV infections in this age group are common and tend to resolve without treatment.
The randomized controlled study, called HPV FOCAL, enrolled 19,009 women ages 25 to 65, with half receiving an HPV test at first screening and half receiving a Pap test at first screening. The goal of the study was to see if initial cervical cancer screening using HPV testing compared to conventional cytology testing resulted in a reduced number of cases with precancerous cervical changes—specifically, cervical intraepithelial neoplasia grade three or worse (CIN3+)—after 48 months. Each arm of the study required follow-up testing of abnormal results and subsequent treatment of any identified abnormal cervical areas.
The study administrators reported that in the first round of screening, more cases of CIN3+ were found in women who had HPV tests than women who only had Pap smears. After 48 months, fewer cases of CIN3+ were detected in women who had HPV testing compared with those who had Pap smears, possibly because abnormalities were found and treated earlier. The researchers concluded that screening with the HPV test reduces a woman’s likelihood of developing CIN3+ at 48 months, although "further research is needed to understand long-term clinical outcomes as well as cost-effectiveness."
Not all experts agree on the implications of the study's findings. Some medical professionals say the study adds to the growing evidence from previous studies that the HPV test is superior to the Pap smear and adds weight to the argument for getting rid of the Pap smear as a screening test for women ages 30 and over. However, other experts say the HPV FOCUS results fail to answer the question of whether the HPV test alone is better than the current recommendation of using both the HPV test and Pap smear together.
Even so, there may be formal changes in guidelines coming soon. In 2014, the Food and Drug Administration approved an HPV test as a primary cervical cancer screen (use of an HPV test alone). In response, a panel of experts issued interim (temporary) guidance in 2015 for using only HPV testing starting at age 25 as an alternative to Pap smears alone or co-testing. In 2016, the American College of Obstetricians and Gynecologists (ACOG) released a statement that, for women ages 30 to 65, either Pap smears alone or co-testing are still specifically recommended in current guidelines from most major societies but that use of HPV screening alone in women age 25 years or older can be considered as an option.
In October of 2017, the U.S. Preventive Services Task Force revised its prior recommendation of co-testing for cervical cancer screening to propose that women ages 30 to 65 either have HPV tests every five years or a Pap smear every three years, but the update has not yet been finalized.**
It is important to note that HPV tests and Pap smears are screening tools and are not diagnostic by themselves. Any positive or abnormal results must be followed up by additional tests and procedures to make a final diagnosis. And while most cervical cancers are caused by high-risk strains of HPV, the few cancers that are not caused by HPV would be missed by using HPV screening alone.
**Update: On August 21, 2018, the U.S. Preventive Services Task Force finalized its recommendations for cervical cancer screening. For women aged 30 to 65 years, the Task Force recommends three options: screening every 3 years with a Pap smear alone, every 5 years with HPV testing alone, or every 5 years with HPV testing in combination with a Pap smear (cotesting). The Task Force does not recommend one option over the other, instead stating that the goal should be that “women receive adequate screening, regardless of which strategy is used.”