Case Report: First case of synchronous androgen receptor-positive salivary duct carcinoma and prostate adenocarcinoma

Introduction The synchronous occurrence of two androgen receptor-positive (AR+) malignancies with overlapping metastatic patterns is exceedingly rare and poses significant diagnostic and therapeutic challenges. Salivary duct carcinoma (SDC) is an aggressive AR + tumor with a high propensity for early metastasis, whereas low-risk prostate adenocarcinomas (PCa) are often indolent. We report the first case of a synchronous SDC of the right parotid gland and a low-grade PCa, where the origin of osseous metastatic spread was initially unknown. Case presentation A 65-year-old male patient presented with progressive right-sided facial palsy and multiple osseous lesions. Initial histopathological assessment of the parotid mass and assignment of the metastases remained inconclusive. After performing a prostate-specific membrane antigen-positron emission tomography/computed tomography (PSMA-PET-CT) scan, a low-grade prostate adenocarcinoma (PCa) (Gleason 3 + 3) was diagnosed. Further pathological and imaging evaluation revealed an AR+, HER2-low, CK7-positive SDC. The extensive skeletal metastases were attributed to the SDC. Conclusion This case shows the diagnostic complexity of synchronous AR + malignancies with overlapping metastatic profiles and emphasizes the need for integrated clinical, radiological, and pathological assessment to ensure optimal patient management. It highlights the need to biopsy metastatic bone lesions in cases of SDC—especially in older men—to rule out osseous metastases from more frequent carcinomas such as PCa.