Classification and Major Groups
Skeletal tumors display significant diversity. Depending on their tissue of origin, they are divided into three main categories: bone-forming, cartilage-forming, and bone marrow neoplasms.
Basic classification of true tumors:
- Derived from bone tissue: benign (osteomas) and malignant (osteosarcomas).
- Derived from cartilage tissue: benign (chondromas) and malignant (chondrosarcomas).
Additionally, tumor-like lesions (fibrous cortical defect, non-ossifying fibroma) have a favorable prognosis and may resolve spontaneously.
Benign Bone-Forming Tumors
This group is characterized by slow growth, sharp demarcation, and the absence of cellular atypia. However, incomplete surgical removal frequently leads to recurrence.
- Osteoma: a dense lesion with a lobulated surface. Microscopically, it features narrowed bone marrow spaces (replaced by fibroreticular tissue) and a lack of osteoclasts.
- Osteoid osteoma: appears as a granular red mass consisting of interlaced osteoid trabeculae rimmed by active osteoblasts. It is typical for children and adolescents.
- Osteoblastoclastoma (giant cell tumor): typically arises in the epiphysis-metaphysis of long tubular bones in patients aged 20–40 years. On cross-section, the tissue is friable, variegated, and brownish-yellow due to hemorrhages, containing blood-filled cysts and numerous osteoclast-like giant cells. It is capable of destructive growth and metastasis despite its benign status.
Malignant Bone-Forming Tumors
The key representative of this group is osteosarcoma (osteogenic sarcoma). It presents in three histological variants: osteoblastic, chondroblastic, and fibroblastic.
- Central osteosarcoma: the most frequent form, growing within the medullary cavity. It has a yellow-brown color with alternating dense and soft areas (necrosis, cysts). Cells are arranged haphazardly or form a moiré pattern. Hematogenous metastasis and a poor prognosis are characteristic.
- Peripheral osteosarcoma: grows on the bone surface, invading the cortical plate. It appears as a gray-bluish lobulated mass. With radical excision, the prognosis is favorable (except for low-grade variants).
Other sarcomas include bone fibrosarcoma, which forms bundles of atypical collagen fibers, and malignant fibrous histiocytoma (a soft brown mass with areas of necrosis). Both tumors are characterized by aggressive infiltrative growth.
Cartilage-Forming Tumors
- Chondroma: a benign neoplasm composed of hyaline cartilage, most commonly affecting the bones of the hands and feet. Cells are arranged haphazardly with pyknotic nuclei. Secondary changes such as myxoid change, necrosis, and hemorrhage may occur. When located in the center of the bone, it is termed an enchondroma; beneath the periosteum, a periosteal chondroma.
- Chondrosarcoma: the malignant counterpart affecting large flat and tubular bones (ribs, pelvis, sternum). Primary mesenchymal chondrosarcoma is typical for older adults, whereas secondary chondrosarcoma (arising from malignant transformation of a benign chondroma) frequently occurs in younger patients.
The Role of Inflammation in Tumor Development
Malignant bone tumors can arise not only de novo but also as complications of prolonged pathological processes.
For example, chronic hematogenous osteomyelitis (the outcome of acute purulent inflammation) is accompanied by the formation of bone cavities, sequestra, and sinus tracts. The long-term course of this disease can lead to secondary amyloidosis, pathological fractures, and even the development of neoplasms directly within the chronic lesion site.