Introduction: Antrodia cinnamomea (AC) is an extremely rare medicinal fungus native to forested regions of Taiwan. It possesses numerous biological activities, especially anti-tumor effects shown in various in vitro cancer cells and in vivo animal models. However, there are few clinical reports about AC as a treatment for cancer patients. This report attempts to demonstrate the therapeutic effect of dish-cultured AC (DAC) on a small cell lung cancer (SCLC) patient taken orally for an extended duration. Patient concerns: An 88-year-old male with a history of diabetes mellitus and hypertension visited the outpatient department with the symptoms of dyspnea and a cough for two weeks. After a diagnosis of SCLC, the patient declined both chemotherapy and radiotherapy because of the side effects and only accepted supportive care without additional therapy. Diagnosis: Limited-stage SCLC (T4N2M1a, stage IV) after the chest radiograph, computed tomography-guided biopsy, and pathological diagnosis. Interventions: The patient was prescribed DAC with an increasing dosage, from 5 g/d up to 10 g/d DAC, for six months, without radiation or chemotherapy treatment. Outcomes: DAC caused the tumor to shrink substantially. Surprisingly, the patient survived for 32 months without relapse after six months of DAC treatment. Laboratory examinations indicated that the patient’s health had improved significantly, reverting to near normal levels. Notably, he had a good quality of life with a high Barthel index score. Unfortunately, this patient died of septic shock caused by acute cholangitis. Conclusion: DAC may exert an anti-cancer effect, which can lead to tumor regression. This is supposed to be achieved by the combined DAC’s immunomodulatory, anti-angiogenic, anti-metastatic, anti-proliferative, and pro-apoptotic effects mediated through multiple signaling pathways. We propose that DAC can be used as a complementary medicine to prolong the life expectancy and improve the life quality of SCLC patients.