Infection with human papillomavirus and long-term oral contraceptive use lead to an increased risk of a rare form of cervical cancer called adenocarcinoma in situ (ACIS), a suspected precursor of invasive cervical adenocarcinoma.
This conclusion comes from a Hutch study published last month - the largest study to focus exclusively on ACIS, said Dr. Margaret Madeleine, a senior staff scientist in the Public Health Sciences Division and lead author of the study.
Madeleine said that while it's clear that HPV infection is associated with virtually all cases of cervical cancer, specific risk factors have been poorly defined or unknown.
"We know that HPV causes cervical cancer, but not every woman infected with the virus gets cancer," she said. "We'd like to know what factors beyond HPV cause disease."
More than 80 percent of cervical cancers are known as squamous-cell carcinoma. The Hutch study focused on ACIS in part because incidence of invasive adenocarcinoma, particularly in younger women, has risen steadily since in the United States and other countries. An examination of incidence rates of adenocarcinoma in the study shows that while rates of invasive cervical cancer have started to level off, those of in-situ (in-its-place) carcinoma are continuing to increase.
Cervical cancer is typically diagnosed with a Pap smear, a simple screening test for analyzing cervical cells. The American Cancer Society recommends yearly Pap tests for women over the age of 18 and all sexually active women.
Treatment for invasive adenocarcinoma, which can include surgery to remove cancerous tissue, can impair child-bearing. Better understanding of the epidemiology of ACIS, the precursor form of the disease, could lead to improved cancer prevention, potentially minimizing effects on reproduction, Madeleine said.
The Hutch study, which observed 150 women with ACIS and about 650 women healthy women in the Seattle area, examined participants for evidence of HPV in tumor tissue and blood samples and interview responses about oral contraceptive use.
More than 85 percent of ACIS specimens analyzed contained HPV DNA, a number that may be an underestimate since many of the tumors are stored samples and may have degraded DNA. More than half of the HPV-positive samples harbor a strain of the virus called HPV 18.
The group also found that women who had used oral contraceptives for 12 or more years were five times as likely to develop ACIS as women who had never used them.
Madeleine said that the Hutch study reinforces the need for continued monitoring of young women using oral contraceptives to provide crucial data on cervical cancer risk factors.