Ans. is 'c' i.e., Brain o Metastatic bone disease is the commonest malignancy of bones and is much more common than primary bone tumors.o The commonest sites for bone metastases are vertebrae (most common), pelvis, the proximal half of the femur and the humerus.o Extremities distal to elbow and knee are least commonly involved sites.o Spread is usually via the blood stream; occasionally, visceral tumors spread directly into adjacent bones e.g., the pelvis and ribs.o Certain tumors are known to be common sources of bone metastasis.o The following primary tumors are the most common to metastasize in the bone; breast, prostate, lung, thyroid, kidney, and gastrointestinal tract.o The commonest source of metastatic bone disease is carcinoma of the breast.o In males most common source is prostate carcinoma.o Bladder and uterine carcinomas are less common sources.o In children, skeletal metastases originate from neuroblastoma, Ewing's sarcoma, and osteosarcoma.