Melanoma in Segmental Naevus Spilus: A Case Series and Literature Review

Nevus Spilus With Dermatoheliosis: A Histologic Mimicker of Melanoma in Situ at Melanoma Excision Margins

ABSTRACT

Nevus spilus, or speckled lentiginous nevus, is a relatively common lesion that presents at birth or in early childhood. It consists of a background tan patch, which appears similar to a café au lait macule or lentigo simplex on histology, studded with various types of nevi. Rarely, these nevi can undergo malignant transformation to melanoma. When melanoma develops within a heavily photodamaged nevus spilus, evaluating excision margins may be challenging because the combined histologic features of nevus spilus and severe dermatoheliosis can mimic melanoma in situ. We report a case of an elderly man with extensive sun damage who developed malignant melanoma within an occult nevus spilus, resulting in multiple excisions with false-positive margins.

Genetic Abnormalities in Large to Giant Congenital Nevi: Beyond NRAS Mutations

Large and giant congenital melanocytic nevi (CMN) are rare melanocytic lesions mostly caused by postzygotic NRAS alteration. Molecular characterization is usually focused on NRAS and BRAF genes in a unique biopsy sample of the CMN. However, large/giant CMN may exhibit phenotypic differences among distinct areas, and patients differ in features such as presence of multiple CMN or spilus-like lesions. Herein, we have characterized a series of 21 large/giant CMN including patients with spilus-type nevi (9/21 patients, 42.8%). Overall, 53 fresh frozen biopsy samples corresponding to 40 phenotypically characterized areas of large/giant CMNs and 13 satellite lesions were analyzed with a multigene panel and RNA sequencing. Mutational screening showed mutations in 76.2% (16/21) of large/giant CMNs. A NRAS mutation was found in 57.1% (12/21) of patients, and mutations in other genes such as BRAF, KRAS, APC, and MET were detected in 14.3% (3/21) of patients. RNA sequencing showed the fusion transcript ZEB2-ALK and SOX5-RAF1 in large/giant CMN from two patients without missense mutations. Both alterations were not detected in unaffected skin and were detected in different areas of affected skin. These findings suggest that large/giant CMN may result from distinct molecular events in addition to NRAS mutations, including point mutations and fusion transcripts.