Overdiagnosis of Melanoma In Situ

Background/Objectives: The incidence of melanoma in situ (MIS) has increased markedly in several high-income countries, often outpacing invasive melanoma without a proportional rise in mortality. This divergence has raised concerns regarding overdiagnosis, defined as the detection of biologically indolent disease that would not have caused harm if left untreated. This review aims to synthesize contemporary evidence on the overdiagnosis of MIS, focusing on epidemiological patterns, screening-related detection, pathological interpretation, quantitative estimates, and clinical consequences. Methods: A narrative review with systematic search elements was conducted using a structured approach informed by PRISMA principles. PubMed was searched for studies published between January 2017 and March 2026, and eligible studies were selected based on relevance to melanoma overdiagnosis, MIS incidence, screening, and diagnostic variability. Results: The literature consistently demonstrates that increases in melanoma incidence are largely driven by MIS and thin invasive lesions rather than advanced disease. Screening and surveillance preferentially increase detection of low-risk lesions, while variability in dermatopathological interpretation contributes to diagnostic drift. Quantitative studies suggest that a substantial proportion of MIS diagnoses may represent overdiagnosis, exceeding 60-80% in some settings. All of this entails significant direct and indirect social costs in several countries. Conclusions: Overdiagnosis of MIS is a significant and multifactorial phenomenon. MIS represents a heterogeneous entity, and future strategies should focus on improving diagnostic precision, risk stratification, and minimizing harm associated with unnecessary diagnosis.