A mesenchymal tumor refers to a bone tumor or soft tissue tumor that develops directly from the bone or soft tissues. It is named after mesenchyme, which is composed of mesodermal cells that develop into connective tissues, like bone, cartilage, fibrous tissue (tendon and ligament tissue), blood vessels, nerves, fat. Mesenchymal tumors can be benign bone tumors, benign soft tissue tumors or cancerous bone or soft tissue tumors called sarcomas. The mesoderm or mesenchymal cells differentiate down different pathways and form the various tissue types. The tumors are named according to the type of tissue being produced.