Doing more with less: The challenging diagnosis of polymorphous low-grade adenocarcinoma in incisional biopsy samples

Aims: The diagnosis of polymorphous low-grade adenocarcinoma (PLGA) remains difficult for general pathologists, particularly in cases of small biopsy samples. We aimed to characterize the histopathological spectrum and immunohistochemical aspects by using an accessible immunohistochemical panel of cytoskeletal proteins in limited samples of PLGA. Methods and results: Forty-six patients diagnosed with PLGA in incisional biopsies were identified retrospectively. Seventy-two per cent of patients were women and 28% were men, with a mean age of 55 years. The palate was the most affected site. Grossly, the mean size of the samples was 0.8 cm and 74% of specimens were fragmented. All tumours characteristically displayed the microscopic features of architecturally diverse patterns, infiltrative areas and low-grade cytology. Neoplastic cells were diffusely positive to cytokeratin (CK) 7, vimentin and S100 protein, but only focally positive to CK14 and negative to α-smooth muscle actin (α-SMA), thus lacking myoepithelial differentiation. Conclusions: Microscopic recognition of PLGA is facilitated by a characteristic combination of multiple architectural patterns of growth, infiltration of adjacent tissues and cytological aspects. These features are present even in small biopsy samples. The association of histopathological aspects with CK7, CK14, vimentin, S100 and α-SMA immunoexpression is helpful in reaching the diagnosis of doubtful cases.