Houston study augurs possible shift in hrHPV genotypes

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Anne Paxton

March 2013—First identified in an HIV patient in 1998, HPV 90 is a genotype of the human papillomavirus that, until now, has received little attention. It is not counted as one of the few well-defined high-risk genotypes, like HPV 16 and HPV 18, that are known to cause the majority of cervical cancer cases.

But after studying data from 808 mostly Latina women patients, pathologists at The Methodist Hospital in Houston recently made surprising discoveries that are likely to raise HPV 90’s profile. HPV 90, these researchers found, may be not only more prevalent than previously thought but also a genotype associated with cervical intraepithelial lesions.

“Unexpected high prevalence of HPV 90 infection in an underserved population: Is it really a low-risk genotype?,” newly published online in the Archives of Pathology & Laboratory Medicine (doi: 10.5858/arpa.2012-0640-OA), is the first study to characterize HPV 90 infection in an underserved North American population, says senior author Yimin Ge, MD, a surgical pathologist and cytopathologist at The Methodist Hospital. Very few previous studies included HPV 90, and those that did were conducted outside the U.S. “HPV 90 has never been looked at in a U.S. population.” Nor, Dr. Ge adds, has anyone proved that HPV 90 is related to disease of any type.

Dr. Ge

“Our original idea was we thought that the demographic change in the Houston area would change the prevalence and distribution of HPV genotypes in cervical disease,” Dr. Ge explains. In the last 10 years, the Houston area has seen a 50 percent increase in its Hispanic residents, who now account for about 44 percent of the city’s population. “Due to the significant demographic change, we thought we might find some differences in this particular Latina population compared to the U.S. general population.” As it turned out, the differences went further than he and his colleagues hypothesized.

The women patients in the study were referred to The Methodist Hospital from 84 charity clinics in the greater Houston area for abnormal Pap test results between 2009 and 2011. After performing liquid-based Pap tests, the researchers extracted HPV DNA and amplified it with PCR, then hybridized the samples with an HPV DNA Genotyping Chip Kit, made by the Korean company GoodGene. This genotyping kit simultaneously detects 40 HPV genotypes—many more than the kits approved by the Food and Drug Administration, which can detect a maximum of 14. A Gene­Pix 4000B Microarray Scanner, made by Molecular Devices, was used to visualize the signal.

Based on 2009 recommendations by an expert working group, the IARC (International Agency for Research on Cancer) classification system on cancer places known genotypes of HPV into four groups. The first, Group 1, includes 14 genotypes currently referred to as carcinogenic or high-risk (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68A/68B) because there is evidence they will cause cancer. Groups 2A and 2B are intermediate-risk classifications of “probably carcinogenic” and “possibly carcinogenic.” Last is Group 3, “not classifiable,” with genotypes considered low risk because there are no data. HPV 90 has been assigned to Group 3.

Dr. Ge and colleagues found that, overall, 93 percent of the 808 women in the study were infected with HPV, and most of those had high-risk or intermediate-risk genotypes. But HPV 90 was detected in 32 of the women—four percent of the study population—with all but one of those women having no co-infections with other genotypes. Ten percent of the women infected with HPV 90 had cytologic abnormalities, including one with low-grade SIL with features suspicious for high-grade SIL.

Distribution of human papillomavirus genotypes in cytology diagnostic categories demonstrates an unexpectedly high prevalence of HPV 90 (4%). Approximately 9.4% of the women infected with HPV 90 had abnormal cytology in the same specimen. Abbreviations: ASC-H, atypical squamous cells, cannot exclude high-grade intraepithelial lesion; ASCUS, atypical squamous cells of uncertain significance; HSIL, high-grade intraepithelial lesion; LSIL, low-grade intraepithelial lesion; LSIL-H, low-grade intraepithelial lesion, cannot exclude high-grade intraepithelial lesion; NILM, negative for intraepithelial lesion. (Reproduced with permission, Archives of Pathology & Laboratory Medicine.)

“The hypothesis was that the most frequent HPV genotypes in this cohort would be different from the U.S. general population. We did a very extensive and comprehensive panel for HPV to include many rarely studied genotypes such as HPV 90,” says study co-author Gabriela Quiroga-Garza, MD, a fourth-year pathology resident at The Methodist Hospital. “I looked at different studies and they don’t usually screen for HPV 90.”

A particularly unexpected finding of the study is that the four percent prevalence of HPV 90 in the study population was even higher than the prevalence of many of the well-studied genotypes such as HPV 11, 32, 33, 43, 44, and 68B. “We never expected HPV 90 to be that high, and we are not sure why HPV 90 is high in this cohort. But this is a very, very high-risk population from charity clinics with history of cervical disease and that could have contributed to this result,” Dr. Ge says.

Dr. Schwartz

Study coauthor Mary R. Schwartz, MD, director of anatomic pathology at The Methodist Hospital, also says it’s unclear why HPV 90 was found in this group. “We do know that there is regional variation on HPV types associated with cervical cancer. It varies from Africa to Asia to the U.S. What we don’t know—because it hasn’t been studied—is if the increased prevalence of HPV 90 will be found in other communities with Latina populations.”

It’s far too early, as well, to conclude that HPV 90 belongs in a higher-risk IARC classification. Dr. Ge cautions that many of the HPV genotypes that have been categorized have been intensively studied, and 808 patients, by comparison, is a very small number. “In order to be classified, a genotype has to have a multicenter study including a lot more patients.”

But in addition to a high prevalence, the study found that 31 of the 32 patients who had HPV 90 infection had no co-infection with another genotype, which could mean that HPV 90 is the cause of their cervical disease. “This is a key point of this paper,” says study coauthor Haijun Zhou, MD, PhD, a second-year pathology resident who has spent the last 14 years studying cancer biology in China and the U.S. “These 31 patients don’t have co-infection with other genotypes, but several of them have concurrent dysplasia, so we think HPV 90 may be a causative mechanism.”

Dr. Zhou

However, much research remains to be done, he stresses, pointing out that for HPV 16 and HPV 18, there is not only epidemiological data but also biological data showing they cause cancer. “For HPV 90, this is the first study in a U.S. population. We can make people aware that HPV 90 is a possible cause for cervical disease, but we need more biological data to support this hypothesis.”