Abstract

Cellular neurothekeomas (CN’s) are uncommon benign cutaneous tumours of uncertain histogenesis. Often occurring as flesh-colored papules/nodules on the face/upper extremity of a young adult, they are characterized microscopically by nested or fascicular aggregates of epithelioid and/or spindled cells in the dermis/subcutis. Though known to express certain markers (e.g. NKI/C3, CD10, MITF, etc) their immunohistochemical (IHC) profile is non-specific and they pose a challenge in interpretation. The serendipitous findings of strong CD56 expression and of a rich intratumoral mast cell infiltrate in a recent CN prompted us to explore these features in a local cohort of cases. A retrospective review of 14 cases of CN (diagnosed between 2000 and 2021) was pursued. Validation of the diagnosis, documentation of demographic, clinical, and morphological data, and pursuit of IHC studies (CD56, chromogranin A, synaptophysin, and CD117) were undertaken. The cohort included 8 females and 6 males with a mean age of 36.5. Most (64%) lesions occurred on the head/neck. A “cyst” was suspected in 3 cases (others indeterminate). The morphology, immunophenotype, and clinical behavior of the lesions were as expected for this entity. Strong uniform expression for CD56 was observed in 6 (43%) cases, focal expression was observed in 4 (29%), and negative results were obtained in 4 (29%). All cases lacked synaptophysin and chromogranin A expression. Brisk CD117-positive mast cell infiltrates were observed in 10 (71%) cases. Awareness of the previously under-recognized spectrum of CD56 expression and frequent brisk intratumoral mast cell infiltrates in CN is informative, given their often-tenuous diagnostic profile.

Financial Disclosure: No current or relevant financial relationships exist.