Initial Therapeutic Approach with Pembrolizumab in Synchronous Multiple Cancers, Including Non-Small Cell Lung Cancer, Highly Positive for Programmed Death-Ligand 1 Expression.

Treatment of synchronous multiple primary cancers is clinically difficult. We report four cases of synchronous primary cancers, including advanced and metastatic non-small cell lung cancer (NSCLCs) highly positive for programmed death ligand-1 (PD-L1) expression and initially treated with pembrolizumab. Pembrolizumab was efficacious in 2 patients with NSCLC lesions, followed by chemoradiotherapy for esophageal cancer (case 1) and chemotherapy for gastric cancer (case 2). Both cancers in case 1 showed a complete response for 3 years, while progression of the accompanying gastric cancer resulted in mortality at 20 months in case 2. Both NSCLC and gastric cancer in case 3 failed to respond to pembrolizumab, but the accompanying laryngeal cancer in case 4 showed a complete response, and cytotoxic chemotherapy for NSCLC was continued for 18.0 months. Our clinical experience suggests that pembrolizumab is a useful therapeutic approach for patients with synchronous cancers, including NSCLC that highly expresses PD-L1.