Osteosarcoma overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Overview

Bone cancer is a malignant (cancerous) tumor of the bone that destroys normal bone tissue (1). Not all bone tumors are malignant. In fact, benign (noncancerous) bone tumors are more common than malignant ones. Both malignant and benign bone tumors may grow and compress healthy bone tissue, but benign tumors do not spread, do not destroy bone tissue, and are rarely a threat to life.

Malignant tumors that begin in bone tissue are called primary bone cancer. Cancer that metastasizes (spreads) to the bones from other parts of the body, such as the breast, lung, or prostate, is called metastatic cancer, and is named for the organ or tissue in which it began. Primary bone cancer is far less common than cancer that spreads to the bones.

There are three types of bone cancer:

• Osteosarcoma - develops in growing bones, usually between ages 10 and 25
• Chondrosarcoma - starts in cartilage, usually after age 50
• Ewing's sarcoma - begins in nerve tissue in bone marrow of young people, often after treatment of another condition with radiation or chemotherapy

Osteosarcoma is the most common type of malignant bone cancer, accounting for 35% of primary bone malignancies. There is a preference for the metaphyseal region of tubular long bones. 50% of cases occur around the knee. It is a malignant connective (soft) tissue tumor whose neoplastic cells present osteoblastic differentiation and form tumoral bone.

Classification

Osteosarcomas may be classified into several subtypes based on differentiation, location within the bone, and histological variants.

Pathophysiology

The osteosarcomas may be localized at the end of the long bones (commonly in the metaphysis). Most often it affects the upper end of tibia or humerus, or lower end of femur. On gross pathology, areas of bone formation, hemorrhage, fibrosis, and cystic degeneration on cut surface are characteristic findings of osteosarcoma. On microscopic histopathological analysis, presence of osteoid within the tumor, pleomorphic cells, anaplastic cells, and atypical mitoses are characteristic findings of osteosarcoma.

Causes

There are no established causes for osteosarcoma.

Differential Diagnosis

Osteosarcoma must be differentiated from Ewing's sarcoma, Giant cell tumors, Malignant fibrous histiocytoma, Osteomyelitis, and aneurysmal bone cyst.