The HPV-18 strain of the human papilloma virus doubles the mortality rate from cervical cancer when compared with cancers caused by the most common strain of the virus, HPV-16.
The findings are reported in the April Journal of Clinical Oncology.
A population-based study confirmed several earlier studies that found that mortality rates from cervical cancers caused by HPV-18 -- the second most common cause of the disease -- could be four times as high as those caused by other HPV variants, including HPV-16.
"I think this study potentially has very important clinical implications, as well as implications for basic research," said Stephen Schwartz, PhD, primary author of the study and an associate member of the Fred Hutchinson Cancer Research Center in Seattle.
"What we need to do now is figure out what we can do with this information to help women with cervical cancer live longer," Dr. Schwartz said. "Do we need to treat them differently with different drugs or different doses of radiation, or do we need to follow them more often?"
Cervical cancer is now treated with varying combinations of surgery, radiation and chemotherapy, but not always all three.
"This shows that those with HPV-18 should be considered for the most aggressive treatment possible," said Harmon Eyre, MD, chief medical officer of the American Cancer Society.
HPV type testing is primarily used as a research tool. It will take further studies for such testing to enter the clinical practice.
"This was a retrospective study," Dr. Eyre said. "What we need is a larger-scale prospective trial before it becomes standard of care, but this is certainly a step in the right direction."
The Food and Drug Administration (FDA) has approved a test for HPV as an adjunct to the Pap smear. A test that determines the type of HPV has not yet been approved, but one could be by the end of this year.
Such a test would be most useful as a diagnostic aid to determine treatment strategies for those with cervical cancer. It may turn out to be too expensive to be used as frequently as the Pap smear, and it may increase the number of women who have false-positives and must undergo colposcopy.
"If you use it on every woman who has a Pap smear, it could turn out to be inordinately expensive, and there are many with HPV infection who do not go on to have cervical cancer," said Dr. Eyre. "It is much more feasible to use it on the 12,800 women who are diagnosed every year with cervical cancer."
HPV-18 is so aggressive that it rarely turns up in the precancerous lesions found by the Pap smear -- but it's frequently found in invasive cervical cancer. Apparently, HPV-18 develops into invasive cancer so quickly that the precancerous state is too short to be detected by an annual Pap smear.
There are nearly 100 varieties of HPV, but the most dangerous strains could be prioritized for vaccine development first. Before vaccination, a woman could be tested to determine which strain she may have and which vaccine she needs to prevent it from leading to cervical cancer.
"We don't know yet if such vaccines work," said Dr. Schwartz. "But if they do, there could be a trend toward patients getting their tumors tested to determine what strain of HPV is present, and then vaccinating them against that particular strain."
Dr. Schwartz is currently researching the factors that increase mortality from cervical cancer related to HPV-18.