In Situ Melanoma Collision With a Basal Cell Carcinoma in a Patient With Basal Cell Nevus Syndrome: Clinical and Dermoscopic Features

Basal cell nevus syndrome (BCNS), also known as Gorlin-Goltz syndrome, is a rare autosomal dominantly inherited disorder characterized by the development of basal cell carcinomas (BCCs) from a young age, multiple keratocysts, palmar and/or plantar pits, calcification of falx cerebri, and family aggregations. Other criteria are skeletal anomalies, frontal bossing, cardiac and ovarian fibromas, medulloblastoma, glaucoma, and cleft lip/palate. The disorder is caused by an alteration of the sonic hedgehog signaling pathway, which results in constitutive activity and tumor cell proliferation. Some germline pathogenic variants of these genes, including PTCH1 and SUFU, have been found and are responsible for clinical heterogeneity. Only 2 case reports have described the occurrence of melanoma in patients with BCNS, but neither reported the occurrence of collision lesions [1,2]. Here we present clinical, dermoscopic, and histological features of a collision tumor of BCC and in situ melanoma in a patient with multiple BCCs and BCNS.