A Pitfall of the Androgen Deprivation Therapy for Salivary Duct Carcinoma: Hormonal Therapy-Induced Castrate-Resistant Prostate Cancer

Introduction Salivary duct carcinoma (SDC) is a rare, high-grade salivary gland malignancy. Recently, targeting the androgen receptor (AR) is one of the most promising new therapeutic strategies for AR-positive SDC. Case Review In this report, a 70-year-old man who was diagnosed with an AR-positive SDC underwent androgen deprivation therapy (ADT) as a treatment for recurrence after primary therapy. The ADT well contributed to control of SDC; however, the patient was referred to urologists for urinary hesitancy and slow flow and he was diagnosed as having castration-resistant prostate cancer. Literature Review Since SDC is a rare disease, it has been difficult to establish the most effective therapy. Nevertheless, several papers have reported the clinical benefit of ADT for AR-positive SDC, and the latest version of the National Comprehensive Cancer Network guidelines also states the importance of assessing for the presence of AR in SDC. On the other hand, in the field of urology, it is also known that although ADT is initially effective in prostate cancer patients, prostate cancer often develops into castrate-resistant prostate cancer due to the adaptation of prostate cancer cells to ADT for survival and growth. Conclusion We reported a case of castrate-resistant prostate cancer diagnosed during the ADT for metastatic SDC. The present case emphasizes the importance of screening for prostate cancer at the initiation of ADT treatment and during treatment.