Cervical Screening for HPV-Vaccinated Individuals
Yesterday I shared a few intriguing updates on the HPV-vaccine and the newer finding that more men suffer with cancer in their throats related to the wart virus than women suffer cervical cancer because of it. The same post shared that eighty percent of people will have some sort of exposure to HPV within their lifetime, so while the HPV vaccine is among the more controversial, it really is important that each of us understand the evolving evidence on both the virus and the screening and preventative measures currently recommended.
The human papillomavirus (HPV) is a common sexually transmitted virus, which can cause cancer in the woman's cervix, vulvar, vagina, and on the penis of a man, the anus of both and even the oropharynx or mouth and throat. There are over 100 types of HPV viruses, with 15 anogenital types.
Essentially all cervical cancer is caused by this wart virus and of these about 70 percent are caused by HPV-16 and/or HPV-18. Actual warts though are more often the result of viruses HPV-6 and HPV-11. The pap smear is essentially a screening tool to evaluate the effect of having been exposed to HPV or the wart virus. As experts began to better understand the role of HPV in cervical cancer, the vaccine became a primary method of prevention, initially in young girls, but as oral cancers resulting from this virus surpassed those of cervical cancer, the vaccine became a recommendation for our young boys as well.
Interestingly, as more and more have obtained the HPV vaccine, screening guidelines are again evolving for this particular population. Australia was the first country to introduce a national publicly funded HPV vaccination program and has since introduced primary HPV screening in those who have been vaccinated. Seventy percent of the target population for HPV-vaccination received immunization in Australia resulting in a significant decline in incidence of both high risk HPV-types and anogential warts in both young females and males. Precancerous lesions have also declined first in young women under 18-years-of-age and then women throughout their twenties.
The Pap Smear
Cervical screening with cytology - the Pap Smear - has been the basis for substantial reductions in cervical cancer incidence and mortality in most industrialized countries over the last few decades. There is discussion about transitioning focus from the Pap Smear to prevention through the vaccine, but there are a few issues I question with this strategy in my mind. What about those who aren't vaccinated, and how about those whose vaccine has waned, which will happen for essentially all at about twenty years of age? How does screening really differ if the current recommendation of starting Pap Smear screening at age 21 years, consistent with the timing associated with waning protection from the HPV-vaccine?
There is also discussion about using the HPV test as the sole primary screening test as opposed to using it in conjunction with cytology for screening of women. Several random control trials have been conducted now to evaluate this model, as well as case controlled studies which essentially all concluding data supports transition to HPV screening exclusively in clinical practice.
Researchers have found that women who have been effectively vaccinated with the nonvalent vaccine in the USA, would only require Pap screening every ten years starting at age 30 or 35 years, receiving only about four screenings in their lifetime. Several additional studies evaluating implementation of these evolving recommendations have been performed, each suggesting that into the future, we will see on-going revisions to cervical screening. The US Preventive Services Taskforce has already moved forward with publishing a draft revision of the guidelines for cervical screening which include a recommendation to use HPV as the sole primary screening test in women aged over 30 years; this is currently in the consultation phase.
Self-collection options are yet another potential change for cervical screening, including vaginal swaps that would screen for HPV. This has already shown an uptake in under-screened and unscreened women in several settings. It is anticipated that self-collection would be effective in overcoming cultural and other barriers to cervical screening, and the practical implications are fairly non-trivial. These tests could be made available via mail or distributed by the clinician in the office, yet it doesn't appear discussion has considered offering them over-the-counter, but rather, remain within the jurisdiction of a practitioner's order.
Canfell, K. (2018). Cervical screening in HPV-vaccinated populations. CLIMACTERIC, 21(3), 227-234.