Trastuzumab-deruxtecan shows interesting disease control in a multitreated patient with ERBB2 amplified parotid carcinoma, a case report

Salivary gland tumors are rare and very heterogeneous types of head and neck cancer. Among them, salivary duct carcinoma (SDC) is one of the most aggressive, with poor prognosis and few recommendations for treatment. Numerous targetable mutations have been described in SDC, especially for Human Epidermal growth factor receptor 2 (HER2), up to 56% according to the literature. This target is interesting due to the development of several forms of anti-HER2 therapy in other cancers. Finally, the antibody-drug conjugate trastuzumab-deruxtecan (T-Dxd) significantly improves progression-free survival and objective response rate, with tolerable side effects. Few data have been published concerning anti-HER2 therapies for SDC, mainly concerning T-Dxd, most of the studies described treatment with docetaxel or trastuzumab alone. As patients with SDC are often young and without comorbidities, they receive a few different treatments. That is why case reports about patients with SDC treated by T-Dxd can facilitate molecular testing of these tumors and improve our knowledge about this rare disease. This report describes a 44-year-old man with HER2-positive locally advanced SDC who experienced disease progression just after surgery. Molecular analysis showed positive androgen receptors, <i>MLH1</i> mutation, and HER2 positivity. He had received several different treatments, including endocrine therapy, chemotherapy, immunotherapy, and anti-HER2 therapy. The longest duration of treatment was observed with T-Dxd: 13 months, allowing local treatment of localized progression (cervical lymph nodes, bone metastasis) at the same time. This report and other published data highlight the need for better implementation of recommendations for molecular testing regarding a rare and aggressive salivary tumor. In addition, these data should increase the development of clinical research in this small patient population.