Bone Tumors: Metastatic and Primary

Bone Tumors

Metastatic Tumors

• Metastatic tumors are the most common malignant neoplasms in bone.
• They are more common than primary bone tumors.
• Characterized by multifocality with a predilection for bone marrow sites in the axial skeleton and proximal long bones.
• In adults, over 75% of skeletal metastases come from thyroid, prostate, breast, kidney, and lung cancers.
• In children, metastatic disease commonly comes from neuroblastoma, osteosarcoma, and Ewing sarcoma.
• Bone metastases are often asymptomatic, but clinical effects include pain and osteolysis.
• Osteolysis leads to pathological fractures in long bones, vertebral collapse, and spinal cord compression.
• Metastases are typically osteolytic, however prostate carcinomas sometimes induce reactive bone formation that leads to osteosclerotic metastases.

Primary Bone Tumors

• Bone tumors are classified by the normal cell or matrix they produce.

Bone-Forming Tumors

• A common feature of bone-forming tumors is bone production by neoplastic cells.
• Most bone is deposited as woven trabeculae, except in osteomas, and is variably mineralized.

Osteomas

• Benign bone-forming tumors that include compact osteoma, osteoid osteoma, and osteoblastoma.

Compact/Ivory Osteoma

• Definition and site: Benign bone-forming tumor projecting from the subperiosteal surface of the bone cortex, commonly affecting the skull and facial bones.
• Gross: Bosselated, sessile, and solitary tumors.
• Microscopic: Well-formed compact bone.
• Complications: Cosmetic deformities, pressure, or obstructive manifestations if arising from inner skull or nasal sinuses.

Osteoid Osteoma

• Definition and site: Benign bone tumor in the shafts of long bones of adolescents and young adults.
• Patients experience persistent pain, worse at night, often relieved by aspirin.
• Gross: Round-oval masses of hemorrhagic gritty tan tissue.
• Microscopic: Well-circumscribed nodule of woven bone (nidus) rimmed by osteoblasts, surrounded by vascular loose connective tissue enclosed by reactive sclerotic bone.

Osteoblastoma

• Uncommon solitary tumor involving vertebrae and, to a lesser extent, long bones of the extremities.
• Histologically similar to osteoid osteoma, but larger and not accompanied by nocturnal pain.

Osteosarcoma

• Definition: Malignant mesenchymal tumor where neoplastic cells produce bone matrix.
• Age: Typically occurs before age 20 but can occur in geriatric patients with risk factors such as Paget disease or radiation.
• Site: Located in the medullary cavity of the metaphysis of extremity long bones, generally around the knee.
• Gross: The most common subtype arises in the metaphysis of long bones and is primary within the medullary canal.
• Tumors are large, destructive, tan-white, and gritty because of bone formation, along with areas of hemorrhage.
• Frequently destroys the surrounding bone cortex and produces soft tissue masses.
• Microscopic: Composed of large, hyperchromatic, pleomorphic, mitotically active tumor cells.
• Can exhibit osteoblastic, chondroblastic, or fibroblastic differentiation by producing bone matrix, cartilage, or fibrous matrix.
• Neoplastic bone has a coarse, lace-like pattern with vascular invasion and wide necrosis.
• Clinical Course: Presents as painful, progressively enlarging masses.
• Radiographs show destructive, infiltrative lesions with bone formation, forming a Codman triangle when the tumor breaks through the cortex and lifts the periosteum.
• Bone formation results in a sunray appearance.
• Aggressive with frequent metastasis to the lung.
• Responds well to neoadjuvant chemotherapy, permitting limb-sparing surgery.
• Variants arising from the bone cortex (paracortical osteosarcoma) or periosteum (periosteal osteosarcoma) are less common and have a better prognosis.

Cartilage-Forming Tumors

• Cartilage-forming tumors make up the majority of primary bone neoplasms.
• Benign tumors are considerably more common than malignant ones.

Osteochondroma (Exostosis)

• Affects patients under 20 years of age and both sexes.
• Commonly develops in the metaphyseal region of long bones near the growth plate, especially near the knee.
• Gross: Mushroom-shaped surface protrusions covered by a cap of hyaline cartilage with surface perichondrium.
• Microscopic: Thick cartilaginous cap covering irregularly arranged bony trabeculae.

Chondroma

• Definition and site: Benign tumor composed of hyaline cartilage.
• Enchondromas arise within the medullary cavity of the bones of hands and feet.
• Juxtacortical chondromas arise on the surface of bone.
• Gross: Enchondromas are usually less than 3 cm and translucent gray-blue.
• Microscopic: Well-circumscribed nodules of benign hyaline cartilage.

Chondrosarcoma

• Definition and site: Second most common malignant matrix-producing bone tumor.
• It occurs after osteosarcoma and primarily affects the central skeleton, including the pelvis, shoulders, and ribs.
• Age: Most patients are older than 40 years, predominantly males.
• Gross: Lobulated, gray, glistening, and semitranslucent; necrosis and spotty calcification are frequently present.
• Microscopic: Classified by histology into conventional (90% of cases) and variants.
• Histologic grade, based on cellularity, cytologic atypia, and mitotic activity, correlates with biologic behavior, with most tumors being low-grade.

Tumors of Unknown Origin

Ewing Sarcoma and Primitive Neuroectoderma Tumor

• Definition and site: Malignant bone tumor characterized by primitive round cells without obvious differentiation.
• Second most common bone sarcoma in children, after osteosarcoma.
• Gross: Arises in the medullary cavity, invades the cortex, periosteum, and soft tissue.
• The tumor is soft, tan-white, and frequently contains hemorrhage and necrosis.
• Microscopic: Composed of sheets of uniform small, round cells with scant clear cytoplasm, rich in glycogen.

Giant-Cell Tumor of Bone (Osteoclastoma)

• Definition and site: Locally aggressive, rarely metastasizing neoplasms of epiphyses commonly occurring between ages 20 and 50.
• Gross: More than half arise near the knees and are large and red-brown with frequent cystic degeneration.
• Destroy the bone cortex and are covered by a thin shell of reactive bone.
• Microscopic: Plump, uniform mononuclear cells, along with many osteoclast-like, multinucleated giant cells is within the tumor.
• Focal necrosis, hemorrhage, hemosiderin deposition, and reactive bone may occur.

Aneurysmal Bone Cysts

• Aneurysmal bone cysts may be primary or secondary.
• Primary Aneurysmal Bone Cyst: Benign tumor presenting as a rapidly growing expansile mass in the metaphysis of long bones or vertebral bodies.
• Lesions consist of multiple, blood-filled cystic spaces separated by thin, tan-white septa.
• Secondary Aneurysmal Bone Cyst: Secondary to any other bone abnormality.