Effect of Aspirin on Development of First and Recurrent Primary Cutaneous Keratinocyte Carcinomas in Older Australian Adults: Extended Follow-up of a Large Randomised Controlled Trial.

Keratinocyte carcinomas (KC) are the most frequent cancers diagnosed in Australia and impart the largest economic cost of all cancers. Predisposed individuals tend to develop multiple KC over their lifetime. Data from the ASPirin in Reducing Events in the Elderly (ASPREE) randomized controlled trial with post-trial observational follow up (ASPREE-eXTension) were analysed, to compare the KC incidence among older Australians randomized to daily 100 mg aspirin or placebo, and to determine whether aspirin influenced multiple primary KC development. Participants were linked to the Medicare Benefits Schedule for KC ascertainment; medical history was collected at ASPREE enrolment. A Cox proportional hazards model was used to estimate hazard ratios (HR) for KC incidence, and was adjusted for age, sex and race. The Anderson and Gill recurrent event model compared the incidence of multiple KC between aspirin and placebo groups. Thirteen thousand eight hundred thirty-eight participants (6,850 aspirin treated, 6,988 placebo) were analysed over median 6.8 years (trial period 4.7 years); 36.1% developed a KC and 20.7% developed multiple primary KCs. Randomization to aspirin was not significantly associated with KC incidence, (adjHR = 0.97, 95% CI [0.92 to 1.03], P = 0.31). However, it did decrease the rate of multiple KC development (adjHR = 0.93, 95% CI [0.88 to 0.99], P = 0.02). This post-hoc analysis of a large trial with post-trial observational follow-up showed that aspirin did not influence the incidence, but decreased the rate of multiple KC.