Metastatic disease is more common than primary bone tumors.

multiple myeloma is the most common PRIMARY malignancy of bone (pathoma), so it's not MM.

it's not paget (lack other Sx, would also have sclerotic lesions)

mostly likely renal or lung cancer metast to the bone

I ruled out Paget's because Paget's is usually localized, per FA, Pathoma, B&B. Although this patient definitely fits the demographic picture, prostate cancer is definitely not the only cancer that can metastasize to the bones. Because these are lytic lesions, it's probably some other cancer that's spread to the bones

Chondrosarcoma occurs in the hip or axial skeleton. I'd imagine that it is specifically located in one region rather than multiple lesions throughout the vertebra. Thats why I ruled this out.

I ruled out osteosarcoma and ewing sarcoma based on age alone. These tumors are seen in 15-25 year olds, and the clinical manifestations don't match up.

Paget's disease has an elevated Alkaline phosphatase level, but there would definitely be a sclerotic phase of bone deposition, rather than multiple osteolytic lesions. Besides, on a clinical vignette they would talk about enlarging head size, CN 8 impingement, fractures, etc. Even if you did go this route, paget's disease causes osteosarcoma, not multiple lytic lesions.

This left me with metastatic carcinoma.

I also chose Paget :/ but realized this which I didn't before:

The stages are not uniform across different bones, so you could have some bones that are in the osteoblastic stage, while others are in the lytic stage etc.

orthobullets.com/topic/8040/images/paget's%20bone%20scan.jpg