Abstract
BACKGROUND
The incidence of anal cancer has increased among both men (160%) and women (78%) from 1973 to 2000 in the U.S. The authors conducted a populationโbased caseโcontrol study of anal cancer to examine factors that may account for this increase.
METHODS
Men (n = 119 patients) and women (n = 187 patients) who were diagnosed with anal cancer between 1986 and 1998 in the Seattle area were ascertained through the local Surveillance, Epidemiology, and End Results registry. Control participants (n = 1700) were ascertained through randomโdigit telephone dialing. Participants were interviewed in person and provided blood samples. Archival tumor tissue was tested for human papilloma virus (HPV) DNA, and serum samples were tested for HPV type 16 (HPVโ16).
RESULTS
Overall, 88% of tumors (all histologies) in the study were found to be positive for HPV. HPVโ16 was the most frequent HPV type detected (73% of all tumors), followed by HPVโ18 (6.9%), regardless of gender. However, 97.7% of tumors from men who were not exclusively heterosexual contained HPV DNA. The risk of anal cancer increased among men (odds ratio [OR], 5.3; 95% confidence interval [95% CI], 2.4โ12.0) and women (OR, 11.0; 95% CI, 5.5โ22.1) who had โฅ 15 sexual partners during their lifetime. Among men who were not exclusively heterosexual and women, receptive anal intercourse was related strongly to the risk of anal cancer (OR, 6.8 [95% CI, 1.4โ33.8] and OR, 2.2 [95% CI, 1.4โ3.3], respectively). Current smokers among men and women were at particularly high risk for anal cancer, independent of age and other risk factors (OR, 3.9 [95% CI, 1.9โ8.0] and OR, 3.8 [95% CI, 2.4โ6.2], respectively).
CONCLUSIONS
The high proportion of tumors with detectable HPV suggests that infection with HPV is a necessary cause of anal cancer, similar to that of cervical cancer. Increases in the prevalence of exposures, such as cigarette smoking, anal intercourse, HPV infection, and the number of lifetime sexual partners, may account for the increasing incidence of anal cancer in men and women. Cancer 2004. ยฉ 2004 American Cancer Society.