A malignant tumor of childhood that frequently metastasizes to bone marrow most often is:

b. Neuroblastoma(Ref: Indian J Hematol Blood Transfus. 2011 ;27(2):93-95)The malignancies of prostate, breast, lungs, kidney & thyroid in adults and neuroblastoma and rhabdomyosarcoma in children are the primary tumors which frequently involve bone marrow.