In an elderly man with osteoblastic bone metastases and a proximal femur lesion, the most likely primary cancer is from which organ?

• A. Breast
• B. Lung
• C. Prostate
• D. Kidney

Answer: (C)

Osteoblastic (sclerotic) bone metastases point to a primary cancer that drives new bone formation, rather than bone destruction. Prostate cancer is classic for producing osteoblastic metastases, especially to the axial skeleton and proximal long bones like the femur. In an elderly man, this pattern is highly characteristic because prostate cancer is common in that demographic and tends to seed bone with osteoblast-stimulating activity, forming dense, sclerotic lesions on imaging. By contrast, cancers such as lung and kidney more often cause osteolytic lesions that weaken bone, and breast cancer—though it can be osteoblastic as well—occurs much less commonly in men. Thus the most likely primary organ is the prostate.