Undifferentiated Castration‐Resistant Prostate Cancer Successfully Treated With Carboplatin and Paclitaxel

Introduction Castration‐resistant prostate cancer (CRPC) is a heterogeneous and aggressive disease with limited treatment options, particularly in poorly differentiated cases that lack androgen receptor expression and progress rapidly even under conventional therapies. Here, we present a rare case of poorly differentiated CRPC that exhibited a remarkable response to carboplatin and paclitaxel therapy. Case Presentation A 53‐year‐old man with metastatic, castration‐sensitive prostate cancer (cT3bN1M1b, PSA 9.39 ng/mL, Gleason 4 + 5) underwent androgen deprivation therapy using bicalutamide and leuprorelin. Nine months later, he developed CRPC, despite undetectable PSA levels. A supraclavicular lymph node biopsy revealed a poorly differentiated carcinoma. Immunohistochemistry was negative for PSA and NKX3.1 and positive for CK5/6. These results excluded neuroendocrine carcinoma and supported a diagnosis of undifferentiated carcinoma. Systemic chemotherapy with carboplatin (area under the curve, five) and paclitaxel (200 mg/m 2 ) was initiated. Partial remission was achieved at 2 months, and complete remission was confirmed at 18 months. After 73 cycles, chemotherapy was discontinued, and the patient has remained in remission during follow‐up. Conclusion This case highlights the potential efficacy of carboplatin and paclitaxel in treating poorly differentiated CRPC, suggesting the need for further investigation into platinum‐based regimens for aggressive prostate cancer variants.