If we are to speak strictly, osteosarcoma is not cancer. This is because cancer typically refers to malignant tumors of epithelial tissue, whereas osteosarcoma, like all sarcomas, is a malignant tumor that occurs in connective or muscle tissue. Therefore, their origins are different: osteosarcoma is not cancer; it is a malignant tumor that occurs in bone tissue, commonly found in the distal femur, proximal tibia, and proximal humerus. So, strictly speaking, osteosarcoma is a sarcoma, a malignant tumor that occurs in bone tissue. It is not what one would typically refer to as cancer, which usually pertains to epithelial tissues, such as in cases of skin cancer or breast cancer. Osteosarcoma is therefore classified as a sarcoma, not as cancer.