Novel Finding of PLAG1 Overexpression and COL3A1::PLAG1 Rearrangement in Nevus Lipomatosus Superficialis.

Nevus lipomatosus superficialis (NLS) is an uncommon benign skin lesion and characterized by aggregates of mature adipose tissue ectopically among the collagen bundles of the dermis. The precise etiology of NLS remains poorly understood, and it is classified as a cutaneous hamartoma in the WHO Classification of Skin Tumors, 5th edition. This is a case report of recurrent classical Hoffmann-Zurhelle form of NLS on a 3-year-old male child's hand. Immunohistochemical stains revealed diffusely PLAG1 positive expression in the lesional stellate stromal cells and adipocytes. Ancillary molecular testing by RNA fusion panel showed COL3A1::PLAG1 rearrangement. These findings suggest that some cases of NLS may share genetic alterations with neoplastic processes involving PLAG1 rearrangements.