Exploring salivary duct carcinoma: clinicopathologic features, morphologic spectrum and genetic changes

Abstract

Background Salivary duct carcinoma (SDCa) has been slow in gaining recognition. Awareness, high index of suspicion and clinicopathological correlation are essential for accurate diagnosis. Genetic changes like HER2 amplification and BRAF mutation are being explored in SDCa. Methods Salivary gland malignancies at Royal Prince Alfred Hospital and Sydney Head and Neck Cancer Institute (1989–2014) were reviewed to identify SDCa. Results 22 cases of SDCa were identified predominantly in men, age range 41–88 years, predominantly involved the parotid with size range 15–90 mm. Facial nerve deficit and cervical lymph node metastases were present in 21% and 71% of patients respectively, requiring salivary gland resection with neck dissection. Histologically, the tumours resembled high-grade invasive and in-situ ductal carcinoma of breast. Micropapillary, rhabdoid and mucinous variants were seen. HER2 was positive in 48% and BRAF (V600E) mutation present in 27%. Most patients received adjuvant radio- and chemotherapy. Ten patients died of disease within 6–33 months (median 13 months). Five patients developed local recurrence. Ten patients developed lung, bone, liver, axilla, mediastinal and brain metastases. Conclusion SDCa are aggressive malignancies with a large histopathologic spectrum including micropapillary and sacomatoid variants. HER2 amplification, BRAF mutation detectable by ancillary diagnostic techniques may provide therapeutic options requiring accurate diagnosis.