Successful Treatment of Synchronous Double Lung and Colon Cancers Using Immune Checkpoint Inhibitors.

We herein report a case of successfully treated synchronous advanced cancers: programmed death-ligand1 (PD-L1)-negative squamous cell carcinoma of the left upper lung lobe and adenocarcinoma of the ascending colon. As lung cancer was prioritized as the primary therapeutic target, the patient received a combination of anti-PD-L1 and anti-cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) antibodies, along with chemotherapy (the POSEIDON regimen). This approach proved effective against both lung and colon cancer. Subsequent testing revealed high-frequency microsatellite instability (MSI-H) in the colon cancer. These findings highlight the therapeutic potential of combined anti-PD-L1 and anti-CTLA-4 antibodies in the treatment of PD-L1-negative lung and MSI-H colorectal cancers.