In elderly male patients, which primary carcinoma is responsible for the vast majority of purely osteoblastic (sclerotic) metastatic bone lesions?

Explanation:
Metastatic prostate cancer classically produces densely osteoblastic (sclerotic) lesions in bone. This is due to tumor cells secreting factors like endothelin-1 that stimulate osteoblast proliferation and bone formation. In contrast, renal cell carcinoma and thyroid carcinoma are renowned for producing highly vascular, purely osteolytic 'blow-out' lesions. Breast and lung cancers typically produce mixed lytic and blastic lesions. Reference: Campbell's Operative Orthopaedics, 14th Edition.