Epidermal Growth Factor Receptor (EGFR) Downregulation by Cetuximab in Salivary Duct Carcinoma: A Case Report

Salivary duct carcinoma (SDC) is a high-grade salivary gland cancer with a poor prognosis. Although therapeutic antibodies capable of targeting several proteins expressed in SDC, such as epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2), have been developed, the stability of these antigens during recurrence remains unknown. Herein, we report a case of SDC in the submandibular gland wherein EGFR loss was pathologically confirmed after EGFR-targeted therapy. A 53-year-old man with a right submandibular mass underwent primary tumor resection with ipsilateral radical neck dissection and was diagnosed with SDC along with high EGFR and HER2 expression. Multiple pulmonary metastases appeared five months after the surgery, and the patient received 12 cycles of chemotherapy with paclitaxel and cetuximab. Although most metastatic nodules disappeared with the chemotherapy, a single nodule enlarged 15 months after the treatment. The resection of the pulmonary nodule pathologically confirmed the metastasis of SDC, wherein EGFR expression was downregulated. The patient has remained in remission for seven years after pulmonary metastasectomy without any additional treatment. As selective pressures caused by molecule-targeted therapies may downregulate the expression of the corresponding molecules, pathological examination using the latest tissue samples is ideal for elucidating the biological features of recurrent SDC. Our findings provide valuable insights for developing effective strategies for the treatment of cases with SDC recurrence post molecule-targeted therapy.