Salivary duct carcinoma

Salivary duct carcinomas are a subtype of primary salivary gland carcinomas. Salivary duct carcinomas show high rates of metastasis and recurrence. 

Epidemiology

Salivary duct carcinomas represent 5-10% of salivary gland malignancies and can arise de novo or out of a pleomorphic adenoma ^1,2. They typically arise in males during the 6^th or 7^th decades ³.

Clinical presentation

Clinical presentation can vary depending on disease severity, but patients most often present with a parotid or neck mass. While frequently painless, some patients presenting with salivary duct carcinoma have also reported pain. In advanced disease, patients may present with facial nerve involvement resulting in weakness or paralysis ^4,5. Metastatic spread affecting 30% of patients at presentation and 50-60% patients following diagnosis can present as dyspnoea (lung metastases), bone pain (bone metastases), and right upper quadrant pain (liver metastases) ^6,7.

Pathology

Although radiological and molecular studies are helpful, positive diagnosis of salivary gland carcinoma requires histological studies. 

Histology

Microscopically, salivary gland duct carcinomas resemble breast ductal carcinoma, containing ducts with comedonecrosis ⁸. Tumour cells have prominent nucleoli with moderate to abundant eosinophilic cytoplasm ^8,9.

Location

Previous studies indicate tumour localisation most frequently to the parotid gland, followed by submandibular gland and buccal space ⁵. 

Radiographic features

CT and MR studies prove beneficial in determining localisation and severity of disease^5,16-20. These tumours most commonly appear as a solid mass with ill-defined borders and heterogenous enhancement patterns. Compared with other salivary gland malignancies, salivary gland carcinomas are associated with invasion into adjacent tissue, included, fat, muscle, and skin ¹⁰.

PET

Salivary duct carcinomas are highly ¹⁸F-FDG avid, thus, PET may provide clinically relevant information for neck node investigation and surgical planning ^11,12. Notably, sensitivity and negative predicative value is significantly higher for ¹⁸F-FDG PET compared to CT ¹¹.

Treatment and prognosis

Salivary duct carcinoma is an aggressive malignancy with a high rate of local recurrence. Median overall survival is 79 months, with a five-year disease specific-specific survival of 64% ³. Management of salivary duct carcinoma is based on retrospective studies. Surgical resection of the tumour followed by radiotherapy is a frequent therapeutic choice ^2,13. Surgery including ipsilateral neck dissection has also been used in some patients ¹⁴, although less frequently than resection of the tumour alone. 

Differential diagnosis

Due to the nonspecific radiological appearance of salivary duct carcinoma, differential diagnosis should primary parotid neoplasms, metastatic intraparotid lymph nodes, and more common salivary tumours such as myoepithelial carcinoma ¹⁵. Imaging studies with heterogenous enhancement pattern with cribriform necrosis and invasion into adjacent tissue are more indicative of salivary duct carcinoma.