-Case Reports-

A Case of Metastatic Submandibular Salivary Duct Carcinoma that Completely Responded to Pembrolizumab Monotherapy

Masashi Nakaishi¹, Koji Sakamoto¹, Atsuko Sakanushi¹, Takeshi Matsunobu¹, Mika Terasaki² and Kimihiro Okubo¹

¹Department of Otorhinolaryngology, Head and Neck Surgery, Nippon Medical School, Tokyo, Japan
²Department of Analytic Human Pathology, Nippon Medical School, Tokyo, Japan

Salivary gland carcinoma is a rare cancer and has more than 20 histopathological types. Although chemotherapy has been the mainstay of treatment for unresectable carcinomas such as multiple recurrence and distant metastasis, no standard regimen is available. In this article, we report a case of poorly differentiated salivary duct carcinoma of the submandibular gland with distant metastases that was successfully treated with pembrolizumab monotherapy. A 66-year-old man became aware of a left submandibular mass 2 months before his first visit to our department. A needle biopsy at a previous hospital revealed carcinoma, not otherwise specified. The combined positive score on a programmed death ligand-1 immunohistochemistry test was 1-10%. The patient was referred to our department for further treatment. Computed tomography revealed left level II and IV neck lymphadenopathy, bilateral lung shadowing, and osteolytic changes in the 12th thoracic vertebra. Needle biopsy showed poorly differentiated carcinoma, positive human epidermal growth factor receptor 2, and positive androgen receptor, which suggested salivary duct carcinoma. These findings indicated a diagnosis of submandibular carcinoma T4aN2bM1 stage IVC. Pembrolizumab monotherapy was started, and tumor shrinkage was observed after three courses of treatment. At 1 year, complete response was achieved without adverse events, and treatment is ongoing. Despite a lack of evidence for the efficacy of immune checkpoint inhibitors in salivary gland carcinoma, the present case suggests that some patients might respond to this treatment. Hence, clinical trials are warranted.

J Nippon Med Sch 2023; 90: 356-362

Keywords
salivary gland cancer, pembrolizumab, immune checkpoint inhibitor, distant metastasis

Correspondence to
Koji Sakamoto, Department of Otorhinolaryngology, Head and Neck Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan
k-sakamoto@nms.ac.jp

Received, February 19, 2022
Accepted, May 13, 2022