Background:A history of keratinocyte carcinoma (KC) is a risk factor for further KCs, but population-based studies quantifying the risk are lacking in Australia. We aimed to describe the risk of subsequent KCs after first KCs in the Australian state of Tasmania.

Methods: Tasmanian residents identified in the Tasmanian Cancer Registry with a first histologically confirmed basal cell carcinoma (BCC), squamous cell carcinoma (SCC) or synchronous BCC and SCC (within 3 months) between January 1985 and December 2013 were followed up for at least 5 years for the development of a subsequent KC. Cumulative risk, incidence rates and standardised incidence ratios (SIRs) were calculated.

Results: Those first diagnosed with BCC-only, SCC-only or synchronous BCC and SCC had (i) 5-year cumulative risks of subsequent KCs of 32%, 29% and 51%, (ii) annualised 5-year incidence rates of 8100/100,000 person-years at risk (PYR), 7747/100,000 PYR and 16,634/100,000 PYR and (iii) SIRs of 10.6 (95% CI: 10.5-10.6), 12.5 (95% CI: 12.4-12.6) and 313.0 (95% CI: 305.2-321.1), respectively. Risk estimates increased substantially when multiple (two or more) lesions of any type were diagnosed synchronously.

Conclusions: In the first Australian population-based study to describe the risk of subsequent KCs according to histological types, around one in three Tasmanians diagnosed with first KCs were diagnosed with subsequent KCs within 5 years. The risk of subsequent KCs was higher among those with a history of multiple synchronous lesions, especially if they included both BCC and SCC lesions.