A 64-year-old man was referred from a local clinic with a chief complaint of cough. Computed tomography (CT) revealed a mass comprising a tumor in the right lower lobe and enlarged mediastinal lymph nodes, and a whole-body workup with positron emission tomography-CT showed bilateral lymph node enlargement and cancerous pericarditis. Biopsy with bronchoscopy of the right lower lobe tumor and mediastinal lymph node confirmed the histological findings of small cell lung carcinoma. The clinical diagnosis of extensive-stage small cell lung cancer (ES-SCLC) was confirmed, and first-line treatment with carboplatin, etoposide, and atezolizumab was initiated, followed by tri-weekly atezolizumab thrice. The patient experienced worsening pleural effusion treated with thoracentesis, pleural drainage, and pleurodesis. He also experienced several recurrences, which were managed with second and third-line chemotherapy with nogitecan and amrubicin. He has been receiving third-line therapy for over 30 months since his initial visit and remains stable as of today. The patient experienced an exceptional treatment outcome considering that the prognosis of ES-SCLC remains poor, with a median survival of approximately 10 months with conventional chemotherapies using cytotoxic agents. The use of immune checkpoint inhibitors (ICI) for ES-SCLC as first-line treatment may demonstrate a persistent antitumor effect, and result in improved survival following discontinuation. In conclusion, therapy including ICI for patients with ES-SCLC is a treatment option that shows possibilities in improving survival even after discontinuation.