Klin Onkol 2018; 31(6): 463-464. DOI: 10.14735/amko2018463.
Described for centuries in the equines, especially gray horses, as “equine melanotic disease”, it was later recognized in non-equine animal models and in humans, particularly on non UV-exposed skin. Animal-type melanoma, also known as pigmented epithelioid melanocytoma (PEM), is characterized by nodules and fascicles of epithelioid transformed melanocytes with pleomorphic nuclei and striking pigmentation, dendritic cells, numerous melanophages and, sometimes, lymphocytic infiltrate [1,2]. Up-to-date, only small series have been reported in humans and, therefore, its biological behavior remains unclear [3]. In 2010, Ludgate et al. examined the clinical behavior of 8 cases of equivocal and 14 cases of unequivocal PEM, concluding that it shows a propensity for regional nodal metastases [4]. By systematic review and meta-analysis of the English literature, in 2015, Vyas et al. have identified 190 cases of PEM. The median Breslow depth was 3.8 mm, loco-regional recurrence was found in 15 cases, recurrence with distant metastases in 6 cases and death occurred in 5 patients [5]. Recently, Bax et al. have suggested that the tumor follows an indolent clinical course, with very low risk of spread beyond regional lymph nodes [6]. Given the complexity of the matter, Elder and Murphy proposed a histological categorization of PEM and PEM-like lesions, with distinctive clinicopathological and biologic attitudes [7]. In this review, we briefly highlight the current information about this rare disease.
