A Rare Complication after Adjuvant Atezolizumab Therapy for PD-L1-Positive Non-Small Cell Lung Cancer: A Case Report

In May 2022, atezolizumab, an immune checkpoint inhibitor (ICI), was approved as adjuvant therapy for PD-L1-positive non-small cell lung cancer (NSCLC). Following ICI administration, lymph node swelling due to drug-induced sarcoid-like reactions has been reported as a rare immune-related adverse event (irAE); however, it is difficult to distinguish from cancer recurrence or metastasis solely based on imaging findings. In this report, we present the case of a 76-year-old female who exhibited enlargement of an intrapulmonary nodule with abnormal accumulation on positron emission tomography-computed tomography (PET-CT) during adjuvant atezolizumab therapy. Suspecting lung cancer recurrence, a partial lung resection was performed; however, the final pathological diagnosis revealed normal lymph node swelling characterized primarily by lymphoid follicle formation without granulomas. This suggests the possibility that the lymph node swelling was caused by the excessive activation of lymphocytes, such as cytotoxic T lymphocytes (CTLs), associated with ICI administration. This suggests that CTL-driven reactive hyperplasia is a plausible hypothesis for the lymph node swelling associated with ICI administration, although causality cannot be definitively established from a single case. With the anticipated increase in patients receiving ICI therapy, the number of cases where it is difficult to distinguish between normal reactive lymph nodes and malignant tumors is expected to rise.