A Case of Peritoneal Carcinomatosis After Hyperprogression in Human Papillomavirus-Positive (HPV+) Oropharyngeal Squamous Cell Carcinoma.

Immunotherapy has been shown to provide clinical benefit in selected patients with head and neck squamous cell carcinoma (HNSCC), regardless of human papillomavirus (HPV) infection, and including recurrent/metastatic (R/M) platinum refractory tumors. Hyperprogression is an uncommon negative outcome of treatment with immunotherapy. We present the case of a patient with HPV+ HNSCC who presented hyperprogression after immunotherapy and a rare metastasis location with peritoneal carcinomatosis and subcutaneous nodules. HPV+ HNSCC is related to distant recurrence after a longer interval of time and more diverse metastasis sites compared with HPV- disease. However, the literature on peritoneal metastasis in HNSCC remains limited, with few documented cases. To the best of our knowledge, this is the first case reporting peritoneal carcinomatosis after hyperprogression in HNSCC.