When Prostate Cancer Mimics Multiple Myeloma: Diffuse Bone Marrow Infiltration Revealing Metastatic Prostate Adenocarcinoma With Neuroendocrine Differentiation.

Diffuse bone marrow infiltration is an uncommon manifestation of metastatic prostate adenocarcinoma and may mimic hematologic malignancies such as multiple myeloma, resulting in diagnostic delay. Neuroendocrine differentiation further complicates the clinical presentation because of its aggressive biological behavior and atypical metastatic pattern. We report a rare case of metastatic prostate adenocarcinoma with neuroendocrine differentiation revealed by diffuse bone marrow infiltration. A 59-year-old man presented with diffuse bone pain and pancytopenia and was initially admitted to the hematology department because of suspected multiple myeloma. Bone marrow examination revealed infiltration by malignant epithelial cells, prompting referral for oncological evaluation. Further investigations demonstrated high-grade metastatic prostate adenocarcinoma with neuroendocrine differentiation associated with extensive osteomedullary involvement. The patient received an intensified therapeutic strategy combining androgen deprivation therapy, abiraterone acetate, and platinum-based chemotherapy with docetaxel and carboplatin. This case highlights the importance of considering metastatic prostate cancer in the differential diagnosis of unexplained cytopenia and diffuse bone lesions in male patients. It also emphasizes the diagnostic value of bone marrow examination and the need to recognize aggressive neuroendocrine variants requiring adapted therapeutic strategies.