Four decades of anal cancer in Tasmania, Australia: what do the case data tell us?

BACKGROUND: Anal cancer is a rare cancer analogous to cervical cancer, largely caused by exposure to oncogenic human papillomavirus. We have sought to study this disease in the epidemiologically distinct population of Tasmania.
METHODS: Medical records at all tertiary and secondary referral centres in Tasmania were audited for records with corresponding International Classification of Diseases (ICD)-10 codes. Statistical significances of trends were evaluated using Fisher's exact test, logistic regression or linear regression.
RESULTS: Of ~1350 screening records, 170 cases of anal cancer were found with patient presentation during 1973-2010, corresponding to 132 patients. This cohort was mostly female (66.7%), with squamous cell histology (81.8%) and anal canal primaries (72.0%). Most cases were detected at Stage II or below and the majority remained disease-free after treatment. Relatively few cases had documentation of typical risk factors for anal cancer, such as HIV seropositivity, a history of cancer or smoking. After 2000, there was a trend towards a lower stage at presentation, correlating with an increased 5-year survival. After 2000, no anal margin tumours presented beyond Stage II; nearly half were detected in situ and none were fatal. For anal canal tumours, there was virtually no change in the mean stage at detection or in survival.
CONCLUSION: This is the first case series of anal cancer in Tasmania. We find that in many ways, including symptoms and pathology at presentation, epidemiology is typical. However, our cohort is distinct in its paucity of known risk groups, including HIV-positive people, those with a history of cancer and smokers.