A population-based study of squamous cell vaginal cancer: HPV and cofactors.

BACKGROUND

Little is known about the etiology of in situ or invasive squamous cell cancer of the vagina. It is thought that some vaginal cancers may have the same etiology as cervical cancer. It is also not known whether in situ and invasive vaginal cancer share the same etiologic factors. We conducted a study to evaluate risk factors for in situ and invasive vaginal cancer and their potential relationship to prior exposure to human papillomaviruses (HPV).

METHODS

A population-based case-control study included 156 women with squamous cell in situ or invasive vaginal cancer diagnosed between January 1981 and June 1998 and 2041 control women identified through random-digit dialing in western Washington state. Cases and controls were interviewed in person and provided blood samples; archival tumor tissue was retrieved for cases. Blood samples were tested for antibodies to HPV, and tumor tissue was tested for HPV DNA.

RESULTS

Women with vaginal cancer were more likely to have five or more lifetime sexual partners (OR = 3.1, 95% CI 1.9 to 4.9), to have an early age at first intercourse (<17 years OR = 2.0, 95% CI 1.2 to 3.5), and to be current smokers at diagnosis (OR = 2.1, 95% CI 1.4 to 3.1) than control women. Approximately 30% of all cases had been treated for a prior anogenital tumor, most often of the cervix. Prior hysterectomy was a risk factor only among women who had no history of prior anogenital cancer (OR = 3.9 95% CI 2.5 to 6.1). Antibodies to HPV16 L1 were strongly related to risk of vaginal cancer (OR = 4.3, 95% CI 3.0 to 6.2). We detected HPV DNA in tumor blocks from over 80% of the patients with in situ and 60% of the patients with invasive cancers.

CONCLUSIONS

In situ and invasive vaginal neoplasia have many of the same risk factors as cervical cancer, including a strong relationship to HPV infection. Women who have been treated for a prior anogenital cancer, particularly of the cervix, have a high relative risk, although low absolute risk, of being diagnosed with vaginal cancer.