Unique pathological findings of lung adenocarcinoma after unexpected nivolumab treatment, possible different effects on the primary lesion and metastatic lymph nodes: case report.

A 69-year-old man was diagnosed with cT1aN2M0-stage IIIA lung adenocarcinoma. Chemoradiotherapy, the standard treatment for cN2, stage IIIA adenocarcinoma, was considered impossible due to his renal functional impairment. So surgery was the only radical treatment option and therefore planned. However, a preoperative chest computed tomography (CT) scan performed three months after the first scanning revealed apparent shrinking of the pulmonary nodule. We performed left upper lobectomy and mediastinal lymph node dissection. Pathologically, we confirmed no adenocarcinoma cells in the resected lung specimen. Alternatively, a foreign body granuloma composed of foamy macrophages and cholesterol clefts was observed among fibrous tissue, suggesting a trace of lost tumor after some treatment, whereas viable adenocarcinoma cells remained in the lymph nodes. Six weeks after surgery, the patient developed hypothyroidism as a side effect and confessed to having undergone a preoperative treatment with nivolumab 20 mg per body twice before surgery. Unexpected preoperative nivolumab treatment was effective only on the primary lesion possibly due to intratumoral heterogeneity or insufficient dosage. We present an extremely rare case with unique pathological findings of lung adenocarcinoma after unexpected preoperative nivolumab treatment that was followed by surgery. We histologically confirmed the tumor cells disappearing only at the primary site and remaining at the lymph node. This case report may provide a clue to the future development of induction therapy using nivolumab and surgery. 2019 AME Case Reports. All rights reserved.