The effect of screening on melanoma incidence and biopsy rates

Abstract

Background: Cutaneous melanomas are common cancers in white populations and early detection is promoted as a means of reducing morbidity and mortality. There is concern that increased skin screening is leading to overdiagnosis of indolent melanomas with low risk of lethality. The extent of melanoma overdiagnosis associated with screening is unknown. Objective: We sought to estimate possible overdiagnosis by comparing subsequent melanoma incidence and biopsy rates among people subjected to skin screening with those who were not. Methods: We recruited 43,762 residents of Queensland, Australia aged 40-69 years with no prior history of melanoma, selected at random from a population register in 2010. At baseline, participants completed a comprehensive melanoma risk factor survey, and were asked if their skin had been examined by a doctor in the 3 years prior to baseline. We calculated incidence and relative risk of histologically confirmed melanoma (invasive and in situ) in years 2 to 7 of follow-up, obtained through linkage to the cancer registry. In secondary analyses, we measured biopsy rates in years 2 to 6 of follow-up. We used propensity score analysis to calculate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs). Results: 28,155 (73%) participants underwent skin screening prior to baseline. We observed 967 first incident melanomas (381 invasive) during 197,191 person-years of follow-up. Those screened had higher rates of melanoma (aHR 1.29, 95% CI 1.02-1.63) and subsequent skin biopses (aHR 1.85, 95% CI 1.69-2.04) than unscreened participants. The higher risk associated with skin screening was evident for in situ melanoma (aHR 1.45, 95% CI 1.09-1.92) but not invasive melanoma (aHR 1.05, 95% CI 0.72-1.54). In secondary analyses where screening was defined as having a skin biopsy in the first year after baseline, we observed significantly increased risks of melanoma (adjusted aHR 1.53, 95%CI 1.23-1.89) and subsequent biopsies (aHR 2.64, 95% CI 2.46-2.84) relative to those who did not have a biopsy. Conclusions: People who undergo skin screening subsequently experience higher rates of biopsies and melanoma (especially in situ melanoma), even after adjusting for all known risk factors, consistent with overdiagnosis.