Pembrolizumab leading to complete resolution of non-small cell lung cancer and microsatellite instability stable colon adenocarcinoma; two birds one stone

Abstract

Introduction: Staging of non-small cell lung cancer is crucial in predicting patient prognosis and more importantly, determining cancer management. In patients without driver mutations, PD-L1 tumor proportion score evaluation becomes vital in dictating treatment, as immunotherapy can be recommended. These agents have been shown to lead to excellent outcomes, even in patients with late-stage disease. Case Report: A 69-year-old male with a history of chronic obstructive pulmonary disease (COPD) presented with worsening dyspnea found to have lung collapse from a large hilar soft tissue mass causing obstruction of the left mainstem bronchus. After malignancy workup, the patient was diagnosed with non-small cell lung cancer clinically staged as IIIB. An incidental finding of microsatellite instability colon cancer was also found during workup. Pembrolizumab treatment was initiated and led to near resolution of both tumors. Conclusion: Stage IIIB non-small cell lung cancer has an overall poor prognosis. Biomarker testing in our case prior to starting concurrent chemoradiation revealed the malignancy to have a 100% tumor proportion score for PD-L1, the fundamental reason why our patient’s treatment was successful. Based on our findings, we advocate for all patients with non-small cell lung cancer regardless of stage to undergo biomarker testing prior to therapy initiation. Furthermore, the resolution of PD-L1 negative microsatellite instability stable colon cancer after pembrolizumab therapy supports further investigation of the utility and mechanism of PD-1/PD-L1-based therapy in PD-L1 negative colon cancer.