MCCs frequently contain areas that histologically resemble BCC and other more common cutaneous malignancies. This can lead to diagnostic errors, particularly in small fragmented curettage specimens or frozen sections.
Neurofibromatosis is associated with cutaneous melanin pigmentation, but an association with ordinary melanocytic nevi has not been described. This retrospective case‐control study was designed to see if neurofibromas in patients with Neurofibromatosis, Type I (NF‐1) differ from sporadic neurofibromas (SN) in their incidence of associated melanocytic nevi and other histologic features. Slides from 114 NF‐1 were compared with 112 SN. Lentiginous melanocytic nevi were identified over 13 NF‐1 (11%) but no SN (p = 0.00019, Fisher’s test). Compared with other NF‐1, NF‐1 with nevi were more frequently associated with melanocytic hyperplasia, honeycomb infiltration of the subcutis (p < 0.03, Fisher’s test), and a greater number of biopsies (p = 0.04, t‐test). Compared with SN, NF‐1 were more frequently associated with melanocytic hyperplasia, lentigo simplex‐like changes, honeycomb infiltration of the subcutis (p < 0.001, Chi squared test), plexiform neurofibroma and epidermolytic hyperkeratosis (p < 0.03, Fisher’s test). SN more frequently presented as a polyp or papule (p < 0.009). Sebaceous hyperplasia (present in 14% of cases), dermal elastosis (9%), lipomatous neurofibroma (8%), epithelial cysts (4%), and keratin granulomas or folliculitis (3%) were equally common in NF‐1 and SN. This study suggests that there may be a fundamental difference in the potential for melanocytic proliferation in NF‐1 compared with SN.
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