Pathology: Bone Tumors

Pathology of Bone Tumors

• Bone tumors get their names from their cell of origin.
• The most common malignant tumors are secondary bone tumors.

Nomenclature of Bone Tumors

• Osteogenic bone tumors are bone forming: osteoma, osteoid osteoma, osteoblastoma (B), and osteosarcoma (M).
• Chondrogenic bone tumors are cartilage forming: chondroma, osteochondroma (B), and chondrosarcoma (M).
• Fibrogenic bone tumors are fibrosarcomas.
• Vascular bone tumors are heamangiomas and angiosarcomas.
• Neurogenic bone tumors are schwannomas.
• Lymphoid bone tumors are Non-Hodgkin lymphomas.
• Bone tumors of unknown origin are Ewings sarcomas and giant cell tumors.

Osteoma

• Osteomas originate from osteoblasts.
• Usually occurs in the craniofacial bones.
• They typically occur in people aged 40-50 years.
• Have a solitary and firm gross appearance.
• Microscopically consist of mature Lamellar bone.
• Asymptomatic and can cause obstruction of the paranasal sinuses or visual disturbances.

Osteoid Osteoma

• Osteoid Osteoma often occurs in the diaphysis of long bones like the tibia or femur.
• Primarily affects young individuals aged 10-20 years.
• Clinically, is painful due to prostaglandin E2 production and respond well to aspirin.
• Grossly appears soft in consistency and are less than 2 cm in size.
• Under a microscope, you can see woven bone with osteoblastic rimming.

Osteoblastoma

• Shares similarities with osteoid osteoma in its microscopic features.
• The usual location is within the vertebral column.
• Tumors are greater than 2cm.
• Does not respond to aspirin.
• Osteoblast rimming is not exhibited

Osteosarcoma

• The most common primary malignant tumor of bone.
• Genetic causes can involve MDM2 genes.
• Secondary causes can be Paget’s disease and radiation.
• Common sites are the metaphysis of the long bones, the knee (60%), pelvis (15%), and the shoulder (10%).
• Affects young individuals aged 10–25 and older adults with 2° osteosarcoma.
• Symptoms include progressive swelling and pain, and can result in pathological fractures (like osteomyelitis).
• Metastatic effects often affect the lungs.
• On gross examination, the tumor is a bulky, gray-white, infiltrative mass that destroys the surrounding cortex and produces soft tissue mass.
• Cut sections will have areas of hemorrhage, necrosis, and cystic degeneration.
• Sheets or nests of malignant osteoblasts, pleomorphic cells with hyperchromatic nuclei and atypical mitotic figures are seen under a microscope.
• The Lace-like osteoid matrix is also visible
• X-rays show Codman triangles (from elevation of periosteum) and Sun ray appearances (due to calcium deposition along the blood vessels extending between the tumor mass and the periosteum).

Chondroma

• Chondromas typically affect individuals aged 20-50 years.
• Frequently found in small bones, particularly in the hands and feet.
• Grossly, small in size (less than 3 cm) and have a lobulated appearance.
• Arose from the medulla, otherwise known as enchondroma, or cortex, juxtacortical chondroma.
• Ollier disease is associated with multiple enchondromatosis.
• Microscopically, mature chondrocytes inside lacunae surrounded by a pale blue hyaline matrix are observed.

Osteochondroma

• Bone exostosis with a cartilage cap.
• Most commonly found in the metaphysis of long bones (epiphyseal cartilage),.
• They originate due to mutations in the EXT1 or EXT2 gene.
• It typically occurs in individuals aged 10–20 years, and stops growing after puberty.
• Grossly are exophytic, fungating (mushroom-shaped) masses with a stalk and cartilage cap.
• Microscopic examination reveals mature bone with a cartilage cap, and marrow elements may be found within the bony stalk.

Chondrosarcoma

• Occurs in the shoulder, pelvis, and ribs.
• Affects individuals aged 40-60 years.
• Involves related genes: IDH1, IDH2, and COL2A1.
• The gross appearance is a bulky, lobulated, gray-white glistening tissue that destroys the surrounding cortex and produces soft tissue mass.
• Microscopic examination reveals atypical malignant chondrocytes (binucleated or multinucleated) with variable polymorphism and mitosis.
• There is focal calcification.
• The X-ray image shows a lytic lesion with a salt and pepper appearance, and the calcified cartilage appears as foci of densities.

Ewing Sarcoma

• Pathogenesis occurs with t(11;22) translocation.
• Usually appears in individuals 10-20 years of age.
• Site is the diaphysis of long bones
• Symptoms can be swelling, pain, and hotness (like osteomyelitis).
• The prognosis for this cancer is very poor.
• Microscopy shows sheets of small, round, blue uniform cells of scant cytoplasm, round nuclei, and microscopic nucleoli.
• Cells will form Homer-Wright rosettes (round groupings of cells with a central fibrillary core).
• Is detected in immunohistochemistry with CD 99.
• X-rays reveal an onion skin appearance (subperiosteal reactive bone formation).

Giant Cell Tumor / Osteoclastoma

• More common in females.
• Site is within the epiphysis of long bones around the knee.
• Microscopic observation shows red-brown mass with cystic degeneration.
• The cortex is thinned, Eggshell crackling sensation is observed.
• Multinucleated giant cells (reactive) in a background of mononucleated stromal cells (tumor cells) are microscopically present.
• Grades indicate malignant potential
• Grade 1 is benign and exhibits predominant giant cells.
• Grade 2 is locally malignant and exhibits predominant stromal cells.
• Grade 3 is malignant and stromal cells showing malignant criteria is observed at this stage.

Secondary Bone Tumors

• Secondary bone tumors are more common than primary bone tumors.
• They are more common in older patients.
• Common primary sites include the prostate and breast.
• The nature is usually either osteolytic or osteoblastic
• Nearly all bone metastases are osteolytic, besides in the prostate which is osteoblastic.
• Multifocality occurs, involving the axial skeleton, especially the vertebral column.

Tumor-Like Conditions

• Aneurysmal Bone Cyst - Blood filled cystic spaces and multinucleated giant cells are observed.
• Fibrous Dysplasia - Localized developmental arrest of bone leads to fibrosis and curved trabeculae (Chines letter appearance).
• Non-Ossifying Fibroma - Very common in children older than 2 years and storiform fibroblasts with some giant cells are observed.