Dedifferentiation of adenoid cystic carcinoma: report of a case implicating p53 gene mutation.

Adenoid cystic carcinoma is an indolent tumour with an unfavorable long-term prognosis. Dedifferentiation of adenoid cystic carcinoma, which is associated with an accelerated clinical course, has recently been described. We report a case with immunohistochemical and molecular workup to elucidate the likely mechanism of dedifferentiation. The patient, a 64-year-old woman, developed dedifferentiated adenoid cystic carcinoma of the submandibular gland ab initio, accompanied by cervical lymph node metastasis. Histologically, the low-grade adenoid cystic carcinoma merged gradually into an extensive dedifferentiated component that was composed of solid sheets and cords of anaplastic tumor cells with focal gland formation. Immunohistochemically, the dedifferentiated component, but not the adenoid cyst carcinoma component, showed strong overexpression of p53 protein and cyclin D1, as well as a higher Ki67 index. Molecular study confirmed the presence of p53 gene mutation selectively in the dedifferentiated component, suggesting a pivotal role of p53 gene alteration in the dedifferentiation process of adenoid cystic carcinoma.