Clinicopathological significance of androgen receptor, HER2, Ki-67 and EGFR expressions in salivary duct carcinoma

Background Salivary duct carcinoma (SDC) is a highly aggressive disease which often metastasizes to distant sites, and there is no established standard therapy for this systemic disease. Given that SDC is biologically similar to breast and prostate cancer, anti-androgenic receptor (AR) and anti-human epidermal growth factor receptor 2 (HER2) therapies have the potential to exert effects, not only on patients with breast and prostate cancer but also on those with SDC. Methods The expression levels of HER2, epidermal growth factor receptor (EGFR), Ki-67, and AR were assessed in 32 patients with SDC, and their correlations with overall survival (OS) and disease-free survival (DFS) were analyzed retrospectively. SDC was classified into five subtypes using a method similar to that used for breast cancer. Results Anti-AR, HER2, and EGFR were positive in 23 (71.9 %), 14 (43.8 %), and 26 (81.3 %) cases, respectively. One or more of these 3 factors were positive in 30 (93.8 %) cases. The Ki-67 labeling index was greater than 15 % in all cases. While molecular status did not correlate with OS, EGFR and AR positivity were significantly associated with DFS in univariate analysis. Multivariate analysis revealed that EGFR was the only independent predictor of DFS. Conclusions The statuses of some molecules are useful to predict DFS in patients with SDC. Ki-67 overexpression suggests that cytotoxic agents are effective for SDC. Since the majority of SDCs express AR, HER2, and/or EGFR, assessing and targeting these molecules are promising strategies to improve the prognosis of unresectable, metastatic or recurrent SDC, and a classification system according to the molecular expression status may be useful to select appropriate therapy.