Signet‐ring cell change in adenoid cystic carcinoma: a clinicopathological and immunohistochemical study of four cases

Aims Signet‐ring cell ( SRC ) change has not been reported in adenoid cystic carcinoma ( ACC ). The aim of this study was to describe the clinicopathological and immunohistochemical findings in four cases of ACC with SRC s ( ACC ‐ SRC ), in which the relative proportion of the SRC component ranged from 25% to 50%. Methods and results The median age was 58 years (range: 48–81 years), and all patients were women. The involved sites were sinonasal, lip, and submandibular. Two patients developed lung metastasis, and one died of disease 63 months after tumour resection. Neither mucinous nor lipid substances were detected in the SRC s. These showed positive staining for AE 1/ AE 3, cytokeratin 14, and epithelial membrane antigen, which highlighted the intracytoplasmic vacuole borders. The SRC nests were surrounded by myoepithelial cells positive for α‐smooth muscle actin and p63. The SRC s showed similar p53 positivity but lower Ki67 and mitotic indices than the conventional component. SRC s were c‐Myb‐negative. Ultrastructural examination revealed that the intracytoplasmic vacuoles were lumina lined by microvilli. Conclusions ACC ‐ SRC is a non‐mucin‐producing and non‐lipid‐producing phenomenon, possibly related to disturbed differentiation of ductal/luminal cells. This cellular modification in ACC apparently does not change the biological behaviour of the tumour, but it may cause significant diagnostic problems, particularly in incisional biopsies.