Several of my recent blog postings have dealt with viruses that cause cancer. One cancer-causing virus that has been in the news lately is human papillomavirus (HPV), a sexually transmitted virus that can cause cervical cancer. The development of a vaccine that protects women from the specific HPV strains that cause cervical cancer was a major step forward in cancer prevention.
Although it is clear that the vaccine reduces infections with these HPV strains, because of the long time interval between infection and the development of cancer it has not yet been proven that vaccination will decrease the incidence of cervical cancer.
However, according to data presented recently at the annual meeting of the Society of Gynecologic Oncologists (SGO), there is already evidence that vaccination decreases the incidence of abnormal Pap smears and the number of procedures needed to evaluate these abnormal screening tests. This is tremendously important news. The cellular abnormalities detected by a Pap smear are clearly precursors of cervical cancer, so it is extremely likely that a decrease in abnormal Pap smears will directly lead to a decrease in cervical cancer.
The red arrow points to a cancer cell.
But there are other important benefits from decreasing the frequency of abnormal Pap smears. In the words of Dr. Warner Huh, from the University of Alabama, Birmingham, “Very few of us can identify with cervical cancer, but almost every woman in the United States can identify with an abnormal Pap smear.” In fact, in the course of a lifetime, nearly 1 in 3 women will have an abnormal Pap smear and have to deal with both the procedures that are required to investigate the abnormality, and also with the anxiety of believing that she may have cancer. So, clearly, decreasing the rate of abnormal Pap smears would be a huge benefit to all women.
The benefits extend beyond avoiding anxiety and medical tests. There is a societal cost savings as well: According to the SGO, the combined costs of screening and treating cervical abnormalities in the US alone amounts to $4 billion per year. That’s quite an opportunity for cost reductions!
In related news, a report published this past week stated that as many as 1 in 4 teenaged girls in the US has a sexually transmitted infection. The medical blogosphere has been abuzz with this information and its implications.
At first blush, this is a horrifying statistic. After all, when most people think of sexually transmitted infections, they think of gonorrhea, Chlamydia, herpes or syphilis, and it would be awful to imagine that 25% of the teenaged girls in the US have one of these infections. However, HPV is included in the definition of sexually transmitted infections used by this report. As many as 80% of women in the US show evidence of having been infected with HPV at some point. Including HPV infections in the definition of sexually transmitted infections, then, will substantially distort the numbers. After all, by this definition, more than 80% of adult women in the US have an STI! Compared to that, 25% doesn’t seem as bad.
This number does, however, add to the importance of vaccinating girls against HPV. If girls are getting infected in their teenaged years, and if vaccination can prevent infection, abnormal Pap smears, future medical procedures, and hopefully the development of cancer, this suggests that vaccination should happen early (ages 8 or 9?), well before girls become sexually active, in order to maximize the benefits.