BACKGROUND: Cutaneous melanoma in situ (CMIS) is a nosologic entity surrounded by health concerns and unsolved debates. We aimed to shed some light on CMIS by means of a large population-based study. METHODS: Patients with histologic diagnosis of CMIS were identified from the Surveillance Epidemiology End Results (SEER) database. RESULTS: The records of 93,863 cases of CMIS were available for analysis. CMIS incidence has been steadily increasing over the past 3 decades at a rate higher than any other in situ or invasive tumor, including invasive skin melanoma (annual percentage change [APC]: 9.5% versus 3.6%, respectively). Despite its noninvasive nature, CMIS is treated with excision margins wider than 1 cm in more than one third of cases. CMIS is associated with an increased risk of invasive melanoma (standardized incidence ratio [SIR]: 8.08; 95% confidence interval [CI]: 7.66-8.57), with an estimated 3:5 invasive/in situ ratio; surprisingly, it is also associated with a reduced risk of gastrointestinal (SIR: 0.78, CI: 0.72-0.84) and lung (SIR: 0.65, CI: 0.59-0.71) cancers. Relative survival analysis shows that persons with CMIS have a life expectancy equal to that of the general population. CONCLUSIONS: CMIS is increasingly diagnosed and is often overtreated, although it does not affect the life expectancy of its carriers. Patients with CMIS have an increased risk of developing invasive melanoma (which warrants their enrollment in screening programs) but also a reduced risk of some epithelial cancers, which raises the intriguing hypothesis that genetic/environmental risk factors for some tumors may oppose the pathogenesis of others.
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