These special histologic subtypes are characteristically negative for ER, PR, and HER2 (triple negative), and include adenoid cystic carcinoma, mucoepidermoid carcinoma, acinic cell carcinoma, and polymorphous low-grade adenocarcinoma.
EGFR was the most expressed TKRs (71%) and it was found across all histotypes. c-Kit expression was mainly restricted to adenoid cystic carcinoma (78%) while HER2 expression, mostly sustained by gene amplification, correlated with salivary duct carcinoma (SDC) in 44% of cases and adenocarcinoma, not otherwise specified (AD, NOS) in 21% of cases.
Limited evidence suggests that p53 abnormalities in combination with HER-2/neu overexpression or loss of pRb expression may have a role in dedifferentiation of adenoid cystic carcinoma.