Multiple myeloma diagnosed during hormonal therapy for prostate cancer: report of two cases

Case 1: A 73-year-old man presented with a serum prostate specific antigen (PSA) level of 30.2 ng/ml, and was diagnosed with prostate cancer (cT3aN0M1, stageD2), for which hormonal therapy (maximal androgen blockade : MAB) was commenced. Nine months later he developed back pain, and osteolytic bone lesions progressed despite a stable, low PSA level (0.087 ng/ml). He was diagnosed with multiple myeloma on the basis of positive M protein on immunoelectrophoresis. MP combination therapy (melphalan and prednisolone) was commenced, but the patient died of multiple myeloma 33 months later. Case 2: A 70-year-old man was diagnosed with prostate cancer (PSA 19 ng/ml) at another hospital 5 years ago, and underwent hormonal therapy (luteinizing hormone-releasing hormone (LHRH) agonist only). He was referred to our hospital and underwent bicalutamide+MAB combination therapy due to a raised PSA level (58 ng/ml) and multiple bone metastases. His PSA level dropped to around 20 ng/ml, but 2 years later he developed back pain, and bone metastases with osteolytic change were seen in the skull, ribs, and limbs. Needle aspiration biopsy of a fist-sized soft tissue mass in the chest wall showed multiple myeloma. Although chemotherapy with melphalan was commenced, the patient died of multiple myeloma 8 months after its diagnosis. Both these cases exhibited rapidly progressing bone lesions, regardless of an absence of any large fluctuations in serum PSA levels, during hormonal therapy for prostate cancer. Further investigations yielded the diagnosis of multiple myeloma. If progression of bone lesions does not match the status of prostate cancer as surmised from the serum PSA level, we should consider the possibility of multiple myeloma, and biopsy of one of the bone lesions.