Malignant pilomatricoma: causes, symptoms, diagnosis, treatment

Malignant pilomatricoma (syn.: pilomatricarcinoma, calcified epitheliocarcinoma, malignant pilomatricoma, trichomatrical carcinoma, pilomatrix carcinoma) is a very rare tumor that occurs as a nodule, usually on the skin of the trunk or extremities in middle-aged people and does not have pathognomonic clinical signs.

Pathomorphology of malignant pilomatricoma. Under the epidermis, often eroded, in the dermis there are matrix cell complexes of various sizes and configurations, often reaching the subcutaneous adipose tissue. Necrotic foci are often visible inside the complexes. The second population of tumor cells are the so-called shadow cells, which in some places form a natural continuation of matrix cell complexes, and in some places form separate structures. Neoplastic matrix cells are characterized by the presence of atypical nuclei, nucleoli, and coarse chromatin. Mitotic figures, including pathological ones, are common. The third population of cells in malignant pilomatricoma may be melanocytes.

Differential diagnosis should be made with pilomatricoma. Malignant pilomatricoma is not associated with the infundibulum epithelium, does not have a cystic appearance, and is not surrounded by compacted connective tissue. In pilomatricoma, as it evolves, shadow cells begin to predominate over matricoma cells, almost completely replacing them at the final stages. In malignant ilomatricoma, matricoma cells predominate at all stages of development and are surrounded by dense lymphocytic infiltrates, which are absent in pilomatricoma.