Osteosarcoma, the most common bone cancer, usually happens to people ages 10 to 30 and most often starts in the arms, legs, or pelvis. Ewing sarcoma also is more likely to be in kids and young adults. It starts most often in the arms, chest, legs, pelvis, and spine. People over 40 are more likely to have chondrosarcoma -- usually in the arms, legs, or pelvis. Cancers like leukemia that start in marrow -- tissue in some of your bones -- aren’t seen as bone cancer.