Abstract and Introduction
Background: Cutaneous melanomas are common cancers in white-skinned 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.
Objectives: To estimate possible overdiagnosis by comparing subsequent melanoma incidence and biopsy rates among people subjected to skin screening 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 2–7 of follow-up, obtained through linkage to the cancer registry. In secondary analyses, we measured biopsy rates in years 2–6 of follow-up. We used propensity score analysis to calculate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs).
Results: In total, 28 155 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 (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.
Cutaneous melanoma is a common and typically highly visible cancer, the incidence of which has been rising rapidly in many populations. Melanoma survival is correlated inversely with tumour thickness. Early detection is promoted as a compelling strategy for reducing the burden of melanoma;[2,3] however, early-detection programmes provide benefit only if they reduce morbidity or mortality from this disease. To date, Germany is the only country in which a population-based programme has been introduced for the early detection of melanoma and other skin cancers, although it remains an open question whether or not the programme has delivered mortality benefits. While there is no systematic programme for the early detection of melanoma in Australia, whole-body skin examinations are commonly offered by primary care physicians, and there are many medical practitioners whose sole clinical activity is 'skin cancer detection and treatment'. As such, a sizeable proportion of the Australian population undergoes regular screening for melanoma and skin cancer each year.
There is concern that increased diagnostic scrutiny (including frequent skin examinations, more biopsies and shifts in pathological thresholds) is leading to the detection of indolent melanomas that would not otherwise have come to clinical attention during the lifespan of the patient, a phenomenon described as the 'cycle of melanoma overdiagnosis'. Overdiagnosis leads to overtreatment, patient harm and inflated costs. In oncology, the strongest evidence for the existence of overdiagnosis comes from long-term follow-up of randomized controlled trials comparing cancer incidence and mortality among participants randomized to screening vs. no screening. Although a pilot trial for melanoma screening has been executed successfully, no large-scale trials with long-term mortality follow-up have yet been conducted, so indirect approaches have been taken to estimate the proportion of melanomas potentially overdiagnosed. For example, descriptive epidemiological analyses using administrative data suggest that up to 50% of melanomas detected may reflect overdiagnosis of otherwise indolent lesions.[8,10–12] While informative, investigations based on aggregate rather than individual-level data can be difficult to interpret because they do not consider a person's inherent risk of melanoma, and they cannot compare melanoma incidence among people exposed to screening or not.
To examine the impact of diagnostic scrutiny on melanoma incidence, we took advantage of a prospective cohort study that was established to explore the incidence and clinical course of cancers of the skin. We hypothesized that patients who underwent screening for melanoma prior to recruitment would subsequently experience higher rates of skin biopsies and melanomas than those who were not screened. We operationalized the screening exposure by categorizing as screened those who had had a skin examination prior to baseline (primary analysis) or a skin biopsy in the first year of follow-up (secondary analysis).
The British Journal of Dermatology. 2022;187(4):515-522. © 2022 Blackwell Publishing