Mammaglobin and DOG‐1 expression in polymorphous low‐grade adenocarcinoma: an appraisal of its origin and morphology

Background Polymorphous low‐grade adenocarcinoma (PLGA) remains a diagnostic challenge for most pathologists due to its large spectrum of histological patterns. In this study, the expression of two new markers recently described for salivary gland tumors was studied in PLGA. Methods The morphology of 33 cases of PLGA was carefully evaluated using hematoxylin‐and‐eosin‐stained sections and confirmed by immunohistochemistry for cytokeratin 7, vimentin, and S‐100. Periodic acid–Schiff with diastase digestion was also used. The expression of mammaglobin and DOG‐1 was carried out using the EnVision System. Mammaglobin was assessed according to the percentage of positively stained tumor cells, while DOG‐1 was evaluated according to its presence and site. For MCM‐2 and Ki‐67, markers of proliferation, the labeling index of cell nuclei positivity was evaluated using total cell number. The ETV6‐NTRK3 fusion was examined by fluorescence in situ hybridization analysis. Results The histological patterns of the tumor were classified as lobular or non‐lobular. For the non‐lobular pattern, tubular, cribriform, glomeruliform, trabecular, and papillary patterns were observed. Mammaglobin was present in all PLGA cases, and its expression was stronger (P = 0.01) in the lobular than in the non‐lobular pattern. The expression of DOG‐1 was present in the apical portion and cytoplasm of the cells. Proliferation markers were low for all cases independent of histological pattern. Conclusions Polymorphous low‐grade adenocarcinoma has been confirmed to originate from the intercalated duct and to feature high expression of mammaglobin in its lobular pattern resembling that of mammary secretory analogue carcinoma, except for the ETV6 gene rearrangement.