[SMALL CELL PROSTATE CANCER PRODUCING SYNDROME OF INAPPROPRIATE SECRETION OF ANTIDIURETIC HORMONE; A CASE REPORT].

A 73-year-old man with progressive prostate cancer visited our hospital after prostate biopsy performed at another hospital. His serum PSA level was 29.02 ng/ml. CT revealed invasion of the bladder, bilateral ureters, and rectum. Otherwise, there was no evidence of metastasis. Pathological findings showed a poorly differentiated adenocarcinoma (Gleason score 4+5) and small cell carcinoma component. Two months after administering combined androgen blockade therapy, he was admitted due to severe hyponatremia caused by the inappropriate secretion of antidiuretic hormone. Furthermore, CT revealed right ureter metastasis, although the PSA levels remained low. Therefore, the patient was put on fluid restriction and sodium administration. After the patient recovered from hyponatremia, chemotherapy, including VP-16 and CDDP, was initiated. However, CT after two chemotherapy cycles revealed disease progression, with multiple bone metastases. Second-line chemotherapy, including CPT-11 and CDDP, was less effective, and the patient died 9 months after the diagnosis.