Partially Dedifferentiated Primitive Malignant Melanoma with Pseudo-Angiomatous Features: A Case Report with Review of the Literature.

Malignant melanoma (MM) is traditionally known as the "great mime" of human pathology, as it is potentially capable of imitating the most disparate neoplasms. It is known that in addition to the more classic histotypes of MM, there are also rare forms, including angiomatoid MM. Similarly, it has been amply demonstrated in the literature that MM is capable of dedifferentiating, losing melanocytic lineage markers, constituting a diagnostic challenge for the pathologist. Although 5 cases of primary angiomatoid MM have been described in the literature, to the best of our knowledge, no cases of dedifferentiated melanoma with pseudo-angiomatoid aspects have ever been described. In this paper, we present a very rare case of partially dedifferentiated MM in which the most dedifferentiated component lost melanocytic lineage immunohistochemical markers and assumed a pseudo-angiomatous morphology. Given the rarity of the case, we carried out a literature review of similar cases described, trying to draw new future perspectives not only about this particular variant of MM but also about the widest field of dedifferentiation/undifferentiation of MM.