Primary Bone Tumors: Classification

• Bone tumors can be classified into two major categories: primary and secondary (metastatic) tumors.

Classification of Major Primary Tumors Involving Bones

• Hematopoietic tumors (40%) can be benign or malignant.
• Myeloma and malignant lymphoma are hematopoietic malignancies.
• Chondrogenic tumors (22%) can be benign or malignant.
• Osteochondroma, chondroma, chondroblastoma and chondromyxoid fibroma are benign chondrogenic tumors.
• Chondrosarcoma, dedifferentiated chondrosarcoma and mesenchymal chondrosarcoma are malignant chondrogenic tumors.
• Osteogenic tumors (19%) can be benign or malignant.
• Osteoid osteoma and osteoblastoma are benign osteogenic tumors.
• Osteosarcoma is a malignant osteogenic tumor.
• Fibrogenic tumors are generally benign, but fibrosarcoma is a malignant variant.
• Giant-cell tumor, unicameral cyst, and aneurysmal bone cyst are tumors of unknown origin (10%).
• Ewing sarcoma is a neuroectodermal tumor.
• Chordoma is a notochordal tumor, originating from benign notochordal cell tumors.

General Features of Bone Tumors

• Benign tumors are more common than malignant tumors.
• Benign tumors typically occur within the first three decades of life.
• Bone tumors in the elderly are more likely to be malignant.
• The cause of most bone tumors is unknown.
• Genetic alterations may play a role in the development of bone tumors.
• Uncommon causes include bone infarcts, chronic osteomyelitis, Paget disease, radiation, and metal prostheses.

Clinical Presentation of Bone Tumors

• Many bone tumors are asymptomatic.
• Bone tumors are often detected incidentally.
• Symptomatic bone tumors may present with pain or a slow-growing mass.
• Sudden pathologic fractures can occur in some cases.

Bone-Forming Tumors: Osteoma

• Types of osteoma include compact osteoma and osteoid osteoma/osteoblastoma.

Compact Osteoma

• Typically occurs in young persons.
• Commonly found in the bones of the skull, vault, face, orbit, and air sinuses.
• Gross features include a non-capsulated, hemispherical (dome-shaped) mass with a broad base, smooth surface, and hard consistency.
• Microscopic features include compact, parallel, and concentric bone lamellae.
• Complications can arise due to pressure on surrounding structures like the brain and scalp.

Osteoid Osteoma

• Affects adolescents and young adults (10-25 years).
• More common in men than women (2:1 ratio).
• Occurs in the bones of the femur and the tibia.
• Gross features include a sharply circumscribed brown or gray lesion that does not exceed 2 cm in diameter.
• Microscopic features include a center of osteoid tissue surrounded by atypical dense calcified bone.
• Symptoms include severe nocturnal pain, which is due to prostaglandin E2 (PGE2) production and can be relieved by salicylates (aspirin).

Osteoblastoma

• Has identical histologic features similar to osteoid osteoma.
• Larger than 2 cm.
• Commonly involves the spine.
• Pain is dull, achy, and unresponsive to salicylates.

Osteosarcoma

• The most common primary malignant tumor of bone.
• It accounts for about 20% of primary bone cancers.
• Follows a bimodal age distribution, with 75% of cases occurring in persons younger than 20 years of age.
• It also has a smaller second peak in the elderly.
• Men are more commonly affected than women (1.6:1).
• Arises from the osteoblast.
• Commonly occurs in the long bones around the knee joint, specifically the upper part of the tibia and the lower part of the femur.
• Originates from the metaphysis.
• On gross examination, osteosarcoma presents as a large mass with specific characteristics.
• It extends within the medullary canal and destroys the cortex.
• The tumor elevates the periosteum, leading to deposition of bony spicules on stretched blood vessels.
• This results in a "sun ray" appearance on X-ray.
• The tumor invades the periosteum and infiltrates the soft tissue.
• Microscopic features include malignant osteoblasts, and spindle cells with cytologic criteria of malignancy.
• It is characterized by a coarse lace-like malignant osteoid matrix.
• Radiological features include a "sun rays" (sun burst) appearance, Codman's triangle.
• Codman's triangle is a triangle of reactive periosteal bone formation between the cortex and elevated periosteum.
• Osteosarcoma can spread locally or hematogenously.
• The lungs, bones, and brain can be affected.

Cartilage-Forming Tumors: Osteochondroma

• The most common benign bone tumor.
• Occurs in late adolescence and early adulthood.
• Men are affected three times more often than women.
• Arises from the metaphysis and around the knee joint.
• Typically found in the lower part of the femur and the upper part of the tibia.
• Can be single (85% of cases) or multiple, sessile or mushroom-shaped.
• Sizes range from 1 to 20 cm.
• Grossly exhibits a small projecting bone covered by a bluish-grey cartilaginous cap.
• Microscopically, it is characterized by a bone covered by a cap of cartilage.
• Complications include pressure on surrounding structures and malignant change, specifically chondrosarcoma.

Chondroma

• Occurs in young age individuals
• Affects the small bones of the hands and feet.
• Most of the cases are asymptomatic and detected incidentally.
• Some are occasionally painful and cause pathologic fracture.
• Generally remains stable.
• Syndrome of multiple enchondromas is known as Ollier disease
• On gross examination, chondromas are usually smaller than 3 cm and can be single or multiple
• the mass is gray-blue and translucent.
• Microscopic features show benign hyaline cartilage with mild cellularity, and small nuclei with small inconspicuous nucleoli.
• Complications include the development of malignancy, which is more frequent with enchondromatoses and rare with solitary chondromas.