The significance of the morphological and immunological characteristics in the diagnosis of parotid mammary analogue secretory carcinoma: five case reports and a review of the literature.

Mammary analogue secretory carcinoma (MASC) of the salivary glands is rarely reported. In this article, the histopathological features of 5 cases of parotid MASC were retrospectively analyzed. AB/PAS and immunohistochemical staining of S-100, mammaglobin and P63 was performed, which were validated by the ETV6-fluorescent FISH detection of NTRK3 gene. The tumors were composed of two kinds of tumor cells. One kind of cells was rich in cytoplasms, transparent or vacuole-like, partial basophilic double tropism, but another type of cellular cytoplasm was acidophilic. The karyotype was consistent between two types of tumors in the vacuolar pattern. Although the tumor cells were arranged in different forms, the cystic (capsule or microcapsule) structures were constantly observed. Two kinds of tumor cells produced different secretions, which were distributed among the tumor cells. Tumor tissues were divided by hardened collagen interstitial, even in the infiltration lesion, collagen and tumor cells mass was also inseparable. The expression of mammaglobin and S-100 significantly differed between the two types of tumor cells. These characteristics contribute to the differential diagnosis of MASC. ETV6-NTRK3 gene detection can be applied in the diagnosis of atypical cases, but it should not be done routinely.