Cutaneous apocrine mixed tumor with intravascular tumor deposits: a diagnostic pitfall.

Apocrine mixed tumor of the skin is a benign adnexal neoplasm usually posing no diagnostic problem for a histopathologist. The purpose of our investigation is to present a small series of 4 benign cutaneous apocrine mixed tumors of the skin that contained small foci of intravascular tumor deposits, a feature not previously described, to the best of our knowledge. The 4 lesions were identified retrospectively after a review of 312 apocrine mixed tumors and 51 eccrine mixed tumors in the collective files of the authors. In all cases, this feature was originally overlooked. The patients were 3 men and 1 woman, ranging in age at diagnosis from 29 to 66 years. Locations included nose (2), forehead (1), and the fifth toe (1). Histopathologically, all 4 neoplasms demonstrated typical features of a benign apocrine mixed tumor; 2 cases were classified as hyaline cell-rich tumors. In all cases, there were either blood or lymphatic vessels containing small intraluminal collections of neoplastic cells, which had the appearances of hyaline cells and immunohistochemically expressed cytokeratins and were partly immunoreactive for S-100 protein and calponin, thus indicating the myoepithelial phenotype. The intravascular location of the neoplastic cells was confirmed by CD31 staining. The nature of the vessels (lymphatics vs. blood vessels) was supported by staining for alpha smooth muscle actin, which stained pericytes in blood vessels. Lymphatic vessels were also stained for D2-40. No eccrine mixed tumor manifested intravascular tumor deposits. Follow-up of the patients revealed no recurrences or metastasis (range: 2-21 years). It is concluded that occurrence of intravascular involvement in benign apocrine mixed tumor of the skin is rare (approximately 1%-2%). This feature is discrete and is easy to overlook. At present, its significance is not completely clear. Until proved otherwise in future, we suggest to consider intravascular deposits in cutaneous apocrine mixed tumors as an innocuous phenomenon.