In the course of a study of borderline melanocytic tumors, we observed a distinctive group of lesions characterized by features very similar to those previously described in the literature as “animal-type melanoma” and epithelioid blue nevus of Carney complex. We have designated these lesions as pigmented epithelioid melanocytoma (PEM). Herein, we present a clinical-pathologic analysis of 41 consecutive PEM from 40 patients and compare them with 11 epithelioid blue nevi from patients with Carney complex. PEM occurred in both sexes of different ethnic backgrounds, including white, Hispanic, black, Asian, and Persian. The median age of occurrence was 27 years (range 0.6–78 years). Tumors had wide distribution with extremities being the most common site. The tumors were formed by deep dermal (mean Breslow's thickness 3.3 mm) proliferation of heavily pigmented epithelioid and/or spindled melanocytes. Five lesions were part of combined nevus. Ulceration was present in 7 cases. Tumor necrosis was present in 1 case. Regional lymph nodes were sampled in 24 cases (59%). In 11 cases, lymph nodes contained metastases (46%). Liver metastases occurred in 1 case. None of the patients died of disease. Clinical follow-up of more than a year (mean 32 months, range up to 67 months) was available in 27 cases (67%). We found no histologic criteria separating metastasizing and nonmetastasizing PEM. Ulceration was the only feature more common in PEM than epithelioid blue nevi of Carney complex. Otherwise, they were histologically indistinguishable. Our data show that PEM is a unique low-grade variant of melanoma with frequent lymph node metastases but indolent clinical course. We suggest that PEM be considered as a provisional histologic entity encompassing both animal-type melanoma and epithelioid blue nevus.
Rare heavily pigmented melanocytic tumors with an indolent but sometimes aggressive behavior and histologic and clinical similarities to equine melanotic disease 16,30,31,51 and melanomas arising in laboratory animals 18,23 have been reported in the literature. 13,14,32,38 These tumors have been referred to as animal-type melanoma. 13,14
The concept of animal-type melanoma in humans is not widely accepted. As no large series of the entity has been reported, definitive histologic criteria allowing unequivocal differentiation of animal/equine-type melanoma from atypical nevi have not been established. Especially intriguing to us was resemblance of human animal-type melanoma to epithelioid blue nevus, initially described in patients with Carney complex, 8 a familial lentiginosis and multiorgan neoplasia syndrome, 9 but also reported in sporadic setting outside the complex. 24,36,37 The appropriateness of the term animal-type melanoma for a human condition was also questioned. Therefore, to avoid arbitrarily designating controversial lesions as melanoma and hoping to refine histologic criteria separating metastasizing from benign lesions, we have instead more recently categorized suspected examples of animal-type melanoma as “borderline melanocytic tumors” under a descriptive rubric of “pigment synthesizing melanocytic tumor.”53 We have later supplanted this term with more appropriate designation, pigmented epithelioid melanocytoma (PEM). We have recommended sentinel lymph node sampling in management of these cases as a “diagnostic procedure” in an attempt to better characterize biologic potential of these tumors, and we began prospectively collecting follow-up information.
Herein, we present a clinicopathologic analysis of 41 consecutive cases of PEM from 40 patients. We also compared our cases with the original series of epithelioid blue nevus from patients with the Carney complex. 8