The new and old in superficial mesenchymal tumors with uncertain origin and/or melanocytic differentiation

Cutaneous myxoma (CM) is an uncommon benign neoplasm of skin, which may be sporadic or arise in association with syndromes such as Carney complex. There has been only one large case series describing CM. We report 54 additional cases of CM; patients had a mean age of 55 years (range = 7–91), with a female-to-male ratio of 1.3. Most occurred on the trunk (n = 19), with the back being the most common site. The remainder presented on the lower extremity (n = 18), head and neck (n = 10), and arm (n = 7). Histopathologically, they were relatively circumscribed, nodular, and centered in the dermis. All had abundant myxoid stroma, a thin, arborizing vascular network, and spindled to stellate cells with no to mild atypia without mitotic activity. Follicular induction, stromal neutrophils, and intranuclear inclusions were present in 35%, 25%, and 61% of cases, respectively. Collagen trapping, splitting of collagen fibers, and encircling of hair follicles or eccrine glands were encountered in a subset. Thirty-nine cases were treated with shave excision, whereas 12 cases underwent wide local excision. Follow-up data were available for 28 of 54 cases (mean = 50 months). Only one case recurred at 36 months. This study suggests CM has a lower risk of local recurrence than previously reported.