Pembrolizumab plus Chemotherapy for Synchronous Multiple Primary Esophageal and Gingival Squamous Cell Carcinomas

Background/Aim: Immune checkpoint inhibitors are effective treatments for a variety of malignancies. However, evidence supporting their use in patients with multiple primary cancers remains limited because these patients are typically excluded from clinical trials. Case Report: We report the case of a 68-year-old man with synchronous squamous cell carcinomas of the esophagus and mandibular gingiva, both with a combined positive score of ≥1 and <10. The patient was treated with pembrolizumab in combination with cisplatin and 5-fluorouracil, resulting in a clinical complete response of the gingival and metastatic lesions and near-complete response of the esophageal tumor. Treatment was well-tolerated, and the patient regained oral intake and body weight. Conclusion: The mechanisms underlying the favorable response remain unclear and may involve factors beyond conventional tumor biomarkers. This case suggests that PD-1 blockade provides a substantial clinical benefit in select patients with multiple primary cancers.