An 80-year-old man presented to the respiratory medicine department at our hospital with bloody sputum. Initial examination revealed hypertension, hypercholesterolemia, and hyperuricemia, but the patient and his family did not have any history of malignancies. Chest CT found no cause for his bloody sputum, and no otorhinolaryngological bleeding was detected by an otorhinolaryngologist. Blood examination results revealed pancytopenia, suggesting malignancy. The patient's serum PSA level 2 years prior to presentation was 2.168 ng/mL but increased to 15.0 ng/mL during a local medical examination 1 month prior to presentation and then again to 44.274 ng/mL upon presentation to our internal medicine department, which prompted referral to our urology department. His serum NSE and soluble interleukin-2 receptor levels were 176 ng/mL and 694 U/mL, respectively. Further examinations revealed normal levels of serum carcinoembryonic antigen, squamous cell carcinoma, carbohydrate antigen 19-9, and pro-gastrin-releasing peptide. Laboratory data suggested the presence of DIC based on the diagnostic criteria established by the Japanese Society on Thrombosis and Hemostasis (2017 edition) (DIC score = 6 [cutoff value, ≥6]; Table ). A rectal examination detected a deep, hard, and irregular mass in the prostate. Abdominal and pelvic CT revealed an irregular mass at the base of the prostate and multiple metastatic lesions in the lymph nodes, bone, and lungs. A bone scan found no significant tracer accumulation. The patient was advised admission for core needle biopsies of the prostate and left iliac bone tumor. The biopsies were performed without any severe adverse events using 12,800 units of thrombomodulin alfa per day, which was administered before each biopsy for a total of two doses. A total of 10 core samples, including four cores from the irregular mass, were obtained from the prostate. Biopsies of the irregular prostatic mass and metastatic mass at the left iliac bone revealed similar small cell NEC, whereas biopsy of the mid-prostate revealed typical adenocarcinoma (Gleason score 3 + 4). Immunostaining characteristics determined from the biopsies suggested that left iliac bone metastasis from a primary NEPC. The patient was ultimately diagnosed with DIC due to primary and metastatic NEPC. Unfortunately, invasive endoscopic examinations, such as a gastroscopy, colonoscopy, and bronchoscopy, could not be performed owing to his physical condition. A comprehensive explanation regarding the disease, its prognosis, and treatment options (ADT, platinum-etoposide chemotherapy, and supportive care) was provided to the patient and his family. However, the patient opted for only supportive care without ADT, stating that he had lived long enough and had suffered from shortness of breath. Accordingly, pain relief treatment using morphine was initiated, with the patient passing away 3 weeks after the biopsies. The family did not consent to an autopsy. At the time of death, the patient's serum PSA and NSE levels were 148.7 and 255 ng/mL, respectively.