Bone tumors - causes, symptoms, diagnosis, treatment, pathology

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Bone tumors occur when bone cells divide uncontrollably, leading to the formation of a mass. Tumors are classified as benign if they remain localized and do not invade surrounding tissues; malignant tumors spread into nearby areas or metastasize through blood or lymph. Malignant tumors can be primary, originating from bone cells, or secondary, having developed elsewhere in the body before spreading to bones. Common sources for secondary tumor cells include breast, prostate, lung, thyroid, and kidney cancers.

Bones consist of various cell types, primarily osteoblasts that create new bone and osteoclasts responsible for breaking down or resorbing bone. Additionally, primitive cells in the bone marrow include human mesenchymal stem cells and neuroectodermal cells, which can differentiate into multiple cell types such as nerve, fat, bone, and cartilage.

The femur, a long bone, consists of two ends known as epiphyses that form joints with other bones. The central section is called the diaphysis or bone shaft. In children and adolescents, there exists a metaphysis between the epiphysis and diaphysis containing the growth plate responsible for bone growth during development. In adults, this growth plate has ossified and fused with both the diaphysis and epiphyses.

Proto-oncogenes are responsible for normal cell growth, but when mutated, they turn into oncogenes that excessively stimulate this growth. To counteract this process, tumor suppressor genes induce apoptosis in mutated cells. However, mutations in either oncogenes or tumor suppressor genes can lead to uncontrolled cell proliferation.

Osteochondromas are the most common benign bone tumors, primarily affecting males under 25. They arise from mutations in the EXT1 and EXT2 genes, which produce proteins essential for synthesizing heparin sulfate that regulates growth plate development. This tumor manifests as a lateral bony projection known as an exostosis with a cap of hyaline cartilage. Osteochondromas typically form in the metaphysis of long bones, especially around the knee joint such as in the distal femur and proximal tibia.

Giant cell tumors primarily affect flat bones such as the ilium and scapula, often developing after bony trauma or radiation exposure. These benign tumors originate from osteoclasts and evolve into multinucleated cells with over 50 nuclei, resembling destructive giants. Typically found in the epiphysis of long bones like the distal femur and proximal tibia, they pose a unique challenge due to their aggressive nature despite being non-cancerous.

Benign tumors such as osteoblastomas and osteoid osteomas originate from osteoblasts. Osteoblastomas feature large nidi over 1.5 cm, while the smaller nidi of osteoid osteomas are less than 1.5 cm and encircled by sclerotic bone tissue that can cause pain through prostaglandin production. Osteoblastomas primarily affect the axial skeleton, particularly the mandible, leading to surrounding bone erosion; in contrast, osteoidosteomas typically occur in long bones like the tibia without significant erosion.

Osteosarcoma is the most prevalent malignant tumor, originating from pleomorphic osteoblasts that excessively produce osteoid tissue. These tumors typically develop in the metaphysis of bones where cell division is active and predominantly affect adolescents. Key mutations associated with osteosarcomas include alterations in the pRB protein, linked to familial retinoblastoma, and changes in the p53 protein related to Li-Fraumeni syndrome.

Ewing sarcoma is a malignant bone tumor primarily affecting adolescents aged 10 to 20, arising from neuroectodermal cells. It features chromosomal mutations, particularly the translocation between the EWSR1 gene on chromosome 22 and FLI1 gene on chromosome 11, leading to an abnormal fusion protein that disrupts cell differentiation. This cancer typically manifests in bones like the femur and sacrum. In contrast, chondrosarcomas predominantly affect older adults and originate from cartilage-producing chondrocytes, commonly impacting pelvic bones as well as long bones such as the proximal femur.

Bone tumors are usually found in the medullary cavity and can lead to symptoms such as bone pain, swelling, and fractures. Osteoid osteoma causes worsening pain at night, while osteochondromas and osteoblastomas may press on spinal nerves resulting in numbness or weakness. If a tumor affects major blood vessels, it can cause avascular necrosis of certain bone areas. Malignant tumors often trigger chronic inflammation leading to fever, night sweats, weight loss; they also have the potential to metastasize to lungs causing pulmonary issues.

Bone tumor diagnosis begins with medical imaging techniques such as X-rays, CT scans, and MRIs. Specific tumors exhibit characteristic findings; for instance, osteochondromas lead to exostoses while giant cell tumors create multicystic lesions resembling soap bubbles. Osteosarcomas present lytic bone lesions known for their sunburst appearance and can lift the periosteum forming Codman’s triangle. Ewing sarcoma is identified by its onion skin appearance on X-ray due to layered periosteal reactions, whereas chondrosarcoma shows patchy lytic areas that give a moth-eaten look.

Bone tumor treatment varies based on malignancy. Benign tumors are typically surgically removed to alleviate pain and prevent fractures. In contrast, malignant tumors require a combination of radiotherapy, chemotherapy, and surgery tailored to the specific case.

Benign tumors include osteochondroma, characterized by exostoses; giant-cell tumor, which appears as soap bubbles on X-ray; osteoid osteoma with a nidus under 1.5 cm; and osteoblastoma with a nidus over 1.5 cm. Primary malignant tumors consist of osteosarcoma featuring large pleomorphic cells and a sunburst appearance on X-ray, Ewing sarcoma presenting round blue cells and an onion-skin pattern, and chondrosarcoma showing multinucleated chondrocytes along with moth-eaten radiographic features. Risk factors for bone tumors encompass rapid growth, trauma to bones, radiation exposure, and family history of such conditions.