Complete and durable response of pulmonary large‐cell neuroendocrine carcinoma to pembrolizumab

BACKGROUND: Pulmonary large cell neuroendocrine carcinoma (LCNEC) is a rare and aggressive tumor with a poor prognosis and standard therapy has not yet been established. CASE: A 65‐year‐old male with a cough for 2 months presented to our hospital. He was clinically diagnosed with non small cell lung cancer cT3N1M0 stage IIIA and underwent right pneumonectomy. The final diagnosis was pulmonary LCNEC pT3N1M0 stage IIIA. Multiple subcutaneous masses were detected 4 months after surgery, and biopsy revealed postoperative recurrence and metastasis. Chemotherapy with carboplatin plus etoposide was initiated. Subcutaneous masses increased and multiple new brain metastases developed after two cycles. Additional tests revealed that epidermal growth factor receptor and anaplastic lymphoma kinase were negative, and the programmed death ligand 1 (PD‐L1) expression rate in tumor cells was 40% (22C3 clones). The primary cells infiltrating the tumor were CD3‐positive T cells and CD138‐positive plasma cells. Second‐line treatment with pembrolizumab was started. The shrinkage of subcutaneous masses was observed after one cycle, and the tumor had completely disappeared after six cycles. Treatment was continued for approximately 2 years. This response has been maintained for 4 years and is still ongoing. CONCLUSION: Pembrolizumab may be used as a treatment option for pulmonary LCNEC.