HER2/HER3-positive metastatic salivary duct carcinoma in the pleural effusion: A case report

Salivary duct carcinoma (SDC) is an aggressive form of salivary gland tumor, and SDC patients tend to be older men, more commonly in advanced stage with a poorer prognosis. Although the cytological characteristics of SDC on fine-needle aspiration cytology have been well-described at the primary site, they have not been explored in metastasis. Here we reported a case of HER2/HER3-positive metastatic SDC in the lung and pleural effusion. The patient was a man in his 50s who had undergone extended total parotidectomy in 2008. He was originally diagnosed as having HER2-positive left parotid SDC. Six years later a mass was discovered in the left lung by chest computed tomography (CT) and was diagnosed as metastatic SDC by both bronchial biopsy and cytology. Subsequently he had a recurrent SDC in the left pleural effusion and died of respiratory failure. Cytological findings from bronchial brushing smear showed small sheet clusters in a slightly necrotic background. In the pleural effusion cytology, tumor cells appeared as ball-like clusters of epithelioid cells with apocrine-like findings. In immunocytochemistry, HER3 of SDC cells in pleural effusion was significantly overexpressed relative to the matched primary tumor, even though HER2 amplification did not change. Cytological findings and HER family receptors differed between the primary and metastatic SDC. Therefore, molecular tests, such as protein expression and gene amplification using cytological specimens, may become important in future when determining therapy strategies in patients with distant metastasis.