Aims: To describe the risk and rate of a subsequent keratinocyte carcinoma (KC) episode (diagnosis more than three months after an index diagnosis) in people with a first-ever KC episode in the Australian island state of Tasmania.
Methods: This prospective cohort study used population data from the Tasmanian Cancer Registry. Tasmanian residents diagnosed with a first histologically confirmed basal cell carcinoma (BCC) and/or squamous cell carcinoma (SCC) between 1 January 1985 and 31 December 2008 were followed-up for 10 years for the development of a subsequent KC episode. Lesions diagnosed within three months of an index date were considered synchronous to the first episode and excluded from the subsequent episode. Cumulative risk, incidence rates and standardised incidence ratios (SIRs) of a subsequent KC episode were calculated according to the histological type(s) of the lesions diagnosed during the first-ever episode (i.e., ‘BCC only’, ‘SCC only’, or ‘BCC and SCC’).
Results: After 10 years, the cumulative risk of a subsequent KC episode was 45% for first episodes with BCC only, 41% for SCC only, and 68% for BCC and SCC. The incidence rate was 6,840/100,000 person-years at risk (PYR) for BCC only, 6,790/100,000 PYR for SCC only, and 14,146/100,000 PYR for BCC and SCC. The SIR was 5.39 (95% CI: 5.36, 5.42) for BCC only, 4.29 (95% CI: 4.25, 4.33) for SCC only, and 8.69 (95% CI: 8.45, 8.93) for BCC and SCC.
Conclusions: The risk and rate of a subsequent KC episode in Tasmanians are high, especially if the first-ever episode included a mix of BCC and SCC lesions. The findings can help with service planning, clinician education, and informing patients of their risk of experiencing a further KC episode depending on the type(s) of lesions diagnosed within the first episode.