Black women are less likely than white women to be affected by the most common strains of human papillomavirus, and may be less likely to benefit from the available HPV vaccines that offer protection, according to new findings from researchers at Duke University School of Medicine.

The findings were presented today at the annual International Conference on Frontiers in Cancer Prevention Research, hosted by the American Association for Cancer Research.

“Screening programs for cervical cancer are known to work well, with around 90 percent of sexually active women getting screened through Pap tests,” said senior author Cathrine Hoyo, associate professor of obstetrics and gynecology at Duke.

“The question is, if screening rates are comparable in African-American and white women, why are the rates of cervical cancer and mortality higher among African-American women when we have a program that works so well?”

Hoyo, a cancer epidemiologist, and her colleagues conduced a small study in Tanzania, the results of which were published in 2011. They found HPV subtypes that were more prevalent in the patient population than those targeted by the vaccine.

With that data in hand, and with funding from the National Institutes of Health, they sought to see if the same differences existed between black and white women in the U.S.

HPV has about 100 different strains. Forty types are spread by sexual contact. The virus causes nearly all cases of cervical cancer, which begin as precancerous cervical abnormalities. A Pap test detects abnormal changes in cells from the cervix.

In 2006, the U.S. Food and Drug Administration approved the Gardasil vaccine to help protect girls and women ages 9-26 against HPV types 6, 8, 16 and 18 – the strains that can cause cervical, vaginal or vulvular cancers, and genital warts. In 2009 the FDA approved the vaccine for use in males ages 9-26 to help protect against genital warts. That same year, the FDA approved the vaccine Cervarix for use in girls and women ages 10-25 to prevent against HPV types 16 and 18, the two strains that account for about 70 percent of all cervical cancers in the United States.

The Duke researchers enrolled 572 participants -- 280 African-American women and 292 non-Hispanic white women -- who came for additional testing after receiving abnormal Pap test results.

Of the group, 239 (42 percent) had early precancerous cervical abnormalities, and 88 (15 percent) had advanced precancerous cervical abnormalities. Seventy-three percent of the women infected with HPV were infected with multiple HPV subtypes.

When looking at specific strains of HPV, they noticed stark differences between white women and black women, with very little overlap. The most frequent HPV subtypes in white women with early or advanced precancerous cervical abnormalities were 16, 18, 33, 39, 56 and 66. In black women the most common subtypes were different: 31, 33, 35, 45, 56, 58, 66 and 68.

Black women in the study had about half as many infections with HPV 16 and 18 as their white counterparts.

Cathrine Hoyo

The findings underscore the importance of having racial and ethnic minorities represented in clinical trials that result in new therapies and preventive treatments, Hoyo said.

“[There weren’t] enough people of African descent,” she said of the trials that led to Gardasil and Cervarix. “We may be rethinking the vaccine itself.”

Added Adriana Vidal, assistant professor of obstetrics and gynecology at Duke’s medical school and the study’s first author: “Since African-American women don’t seem to be getting the same subtypes of HPV with the same frequency, the vaccines aren’t helping all women equally.”

Merck, the maker of Gardasil, has also developed a new HPV vaccine that targets nine HPV subtypes (6, 11, 16, 18, 31, 33, 45, 52 and 58) in women ages 16-26. The company on Thursday announced that it plans to present study results at a conference next week in Italy.

The researchers stress that their findings are preliminary; they already have begun collecting additional data from a larger study population, which they hope will grow to about 2,000 women. They are continuing their research to see if they can define markers that can be used to predict which abnormal cell activity will develop into cervical cancer.

“We are not done yet,” Hoyo said. Just because women who have received the vaccine are protected against cervical cancer caused by the most prevalent HPV strains, all of them - especially black women - also should be concerned about getting protected against the other strains of the virus as well, she said.