Return to CAP Home
Printable Version

  Finding multiple HPV genotypes in adolescent females

 

CAP Today

 

 

 

February 2011
Feature Story

Anne Paxton

New discoveries about human papillomavirus infections in adolescent girls were the focus of an ASM presentation by Janice Matthews-Greer, PhD, professor of research in pediatrics and clinical pathology and director of the diagnostic virology and HPV Diagnostics Laboratories at LSU Health Sciences Center in Shreveport, La.

Dr. Matthews-Greer decided in 2001 to study adolescent HPV after she noticed peculiarities in her laboratory’s test results. “It seemed like we were having a lot of atypical cytology results in our young girls, about 24 percent atypia compared to 10 percent in the adult women. These were shockingly high numbers.”

With LSU’s large indigent patient base, “I thought it was our population, because we have 12- and 13-year-olds who come in pregnant.” But after she pored over charts and tabulated cases of ASC-US (atypical squamous cells–undetermined significance) results and high-risk HPV reporting over the course of a year, “I started wondering if certain types of HPV might be more common in younger girls.” So she obtained funding for a study to pin down specifically which of the more than 130 different kinds of HPV genotypes were infecting the adolescent girls.

“We were in the process of genotyping HPV extracted from old cervical carcinomas and found, for the most part, a single HPV genotype in each tumor block. So, when we started typing the liquid Pap smear specimens from our adolescents and we read off the results from the instrument, I thought we had done something horribly wrong, that we had some kind of contamination. These girls had two or even five different HPV types. But after talking with pediatric and adolescent medicine specialists during poster presentations at meetings, I found we weren’t the only ones finding multiple genotypes in adolescent females.”

Why would an adolescent population be susceptible to a larger number of genotypes? “Their behavior is one factor, but also their anatomy is different,” Dr. Matthews-Greer explains. “The transformation zone is the interface between the two types of cells you find in the endocervix and the ectocervix. This region is highly susceptible to infection. With age, that zone migrates, getting further and further inside the cervix, and additional mucous is produced, so it’s less exposed to infectious agents.”

There’s also evidence that adults have some protection against HPV. “But we really don’t understand it. It might be that we’re all infected early on, then tend to lose the infection, and maybe have to be re-infected before problems arise. But we just don’t understand the immunology of HPV.”

In 2000, LSUHSC staff ordered a Pap test for any patient who was sexually active. Specimens with cytology results of ASC-US or above were reflexed to Dr. Matthews-Greer’s lab for high-risk HPV testing. She used an assay that at the time had 13 probes, so it would detect 13 different high-risk types—those types that are most often found in carcinomas.

Of course, she realized this process was catching only a fraction of HPV infections. “We weren’t testing girls with normal Pap smears. But in most cases, HPV infection is transient; most girls will lose the virus before they develop cytopathology and never have ASC-US. We were only catching the ones developing atypia. Imagine all the ones who never came in for a Pap smear, or who had normal Paps but were HPV-infected as well.”

Special risk factors for HPV include early age of sexual debut and multiple partners, Dr. Matthews-Greer notes. “If women were to wait until the cervix were mature before having sex, they would have some protection that’s provided by nature. Also, if you have multiple partners, you’re more likely to have exposure.” Trauma, since many of the girls’ partners are likely to be older men, could also be part of the picture. These factors are thought to apply to other STIs as well, she notes—probably not just HPV—and might explain some of the high gonorrhea and chlamydia rates found in this age group.

The ALTS trial (ASCUS/LSIL Triage Study) showed that high-risk genotypes of HPV tend to be more persistent, she says. “The ones that are lower-risk tend to be less persistent, and that might be one reason why we see more of the high-risk types in tumors.” Current vaccines cover about 80 percent of the HPV genotypes found in cancers, not necessarily the most prevalent HPV genotypes circulating in any geographic region. “HPV 18 is an example of a genotype that was not common in my population, but it is very common in tumors. So I have to think there might not have been much HPV 18 in our cohort, but when they got it, it was very important.”

Since more than half of the adolescent girls she studied had more than one genotype, when the study showed 58 percent of girls had no type that was included in the vaccine, at first she panicked a little. “I remember arguing with people at meetings, saying we have all these types that aren’t in the vaccine—what are we going to do? But later I realized if it’s rarely found in tumors, then it may not be cost-effective putting it in the vaccine.”

She compares the HPV infection process to a gradual long-term assault. “You have to think of it as a healthy person being hit with all these arrows, but you’re able to pull them out. They keep coming and you continually fight them off.” Some types may be more difficult to remove or some types are just more prevalent. In either case, one might persist.

Older females, as a result, are more likely to have a persistent HPV infection than younger girls. “We obviously have developed a protective immune response to HPV, because a lot of people get infected and there isn’t much cancer out there.” But there is a raft of unanswered questions about HPV that make it seem more complex than gonorrhea or chlamydia, she says. “We assume you can be re-infected with the same genotype, but can you really? If you test positive at one clinic visit for HPV 16 and you test negative at the next two visits, then test positive a year later, were you truly negative and got re-infected with the same genotype, or was the virus present the entire time but just not detectable during that interim?” Those questions seem to apply not just in inner-city Shreveport but in Copenhagen and cities in New Jersey. “It really is a worldwide problem.”

The vaccine developers are focusing on the right genotypes, however. “At first I was upset that Merck went with HPV 6 and 11, which are two low-risk types, instead of adding two additional high-risk HPVs to their vaccine. While HPV 6 and 11 cause up to 90 percent of all genital warts, cancer is the real enemy. I thought it was a waste of money, but in retrospect it was smart marketing, especially now that we are vaccinating boys. These adolescents, if you tell them you’re going to give them a cancer vaccine, they just look at you. If you tell them you’re giving them a vaccine to prevent genital warts, they’ll go for it.”

Dr. Matthews-Greer cautions diagnostic laboratories to remember that “when we turn out a result, the physician is likely to act on it. And not all information is good information.” For one thing, the doctor might perform a colposcopy, “and the majority of young girls don’t need colposcopies.”

The American College of Obstetricians and Gynecologists’ 2009 guidelines recommend no HPV testing and no Pap testing for adolescents, and “here at LSU we go by ACOG, unless we have a really high-risk situation.” But a 2010 survey found that 50 percent of providers were screening 18-year-old virgins, and 80 percent of providers were screening 18-year-olds who initiated sex within the last month. “So lack of awareness, in some cases a tendency to reject the evidence, plus commercial and economic interests at every level, combined with an underestimation of harm from screening too early, unfortunately, are keeping many of us from following the rules,” Dr. Matthews-Greer says.


Anne Paxton is a writer in Seattle.
 

Related Links Related Links