Abstract
RATIONALE: Immune checkpoint inhibitors are generally considered to be ineffective in chemotherapy for anaplastic lymphoma kinase (ALK)-positive lung cancer. We encountered an ALK-positive lung cancer patient who responded well to pembrolizumab. PATIENT CONCERNS: A 70-year-old man presented with a chest shadow. DIAGNOSIS: A mass shadow in the left lower lung field was diagnosed as lung adenocarcinoma cT2N3M1b stage IVA. ALK staining by immunohistochemistry was strongly positive (3+), and fluorescence in situ hybridization detected ALK rearrangements. Immunostaining showed that 95% of tumor cells expressed programmed death ligand-1 (22C3 clones). INTERVENTIONS: First-line therapy with alectinib was initiated, resulting in clinical improvement and a partial response (PR), which progressed after 14 months. The patient continued to receive various medications; however, the tumor gradually increased in size. Therefore, pembrolizumab was initiated as the 8th-line treatment and was effective. OUTCOMES: The tumor shrank after 2 cycles of pembrolizumab, and the patient achieved PR. Nine months later, the patient has maintained PR. LESSONS: Few case reports have described the successful treatment of ALK-positive lung cancer with immune checkpoint inhibitors. We herein present a rare case of ALK-positive lung adenocarcinoma that responded to pembrolizumab monotherapy as the 8th-line treatment.