Re-evaluating historic cohort of salivary acinic cell carcinoma with new diagnostic tools.

Mammary analogue secretory carcinoma (MASC) was recently identified as a distinct salivary gland neoplasm, morphologically resembling intercalated duct cell predominant acinic cell carcinoma (AciCC). To determine how frequently MASC has mimicked an intercalated duct cell predominant AciCC, we reviewed AciCC diagnosed from 1956 to 1975. Nine AciCC consecutively diagnosed in that period were identified. Based on morphologic examination, one case diagnosed as AciCC in a male patient in 1960 was re-classified as MASC [confirmed by fluorescence in situ hybridization (FISH) showing ETV6 translocation]. Another case diagnosed as AciCC of the palate in a female patient in 1975 was re-classified as mucoepidermoid carcinoma (based on the lack of acinar differentiation, presence of mucous cells, and confirmed by FISH showing MAML2 translocation). In this proof-of-principle study, we show that 1 in 9 cases historically designated as AciCC represents a MASC. "Intercalated duct cell predominant AciCC", especially among male patients, most likely represent examples of MASC. For anatomic sites outside of the parotid glands, broader differential diagnoses should be considered before accepting morphologic variants of AciCC as the final diagnosis.