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Risk of subsequent keratinocyte carcinomas after a first diagnosis in Tasmania, Australia.

BACKGROUND/OBJECTIVE
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.