Classification of bone tumors

The classification of bone tumors relies on the cytologic features and products of tumor cells. This classification is reproducible and accepted by pathologists, oncologic surgeons and oncologists. Chondrogenic tumors are the second largest group of bone tumors. Their histologic pattern suggests a relationship to hyaline cartilage. Exostoses, or osteochondromas, represent about 1/3 of chondrogenic lesions. Chondromas are hyaline cartilage tumors which can be found centrally or subperiosteally; they may contain some calcifications and/or ossifications. Chondroblastomas are tumors whose cells produce, at least focally, a matrix similar to hyaline cartilage. Histology of chondromyxoid fibromas shows large or small areas where proliferating cells produce a matrix resembling the hyaline cartilage. Chondosarcomas are tumors whose malignant cells produce a cartilaginous matrix. Most of them occur in previously normal bones; they are classified as conventional or primary chondrosarcomas. Secondary chondrosarcomas result from the malignant transformation of a benign cartilaginous lesion less commonly enchondromas and most commonly osteocartilaginous exostoses, or osteochondromas. Less common variants include dedifferentiated, mesenchymal and clear cell chondrosarcomas. Osteogenic tumors are the third largest group of bone tumors, with osteosarcomas being the most frequent type. The most important criterion for a tumor to be considered an osteosarcoma is that the malignant tumor cells must produce a recognizable osteoid matrix, at least focally. Osteosarcomas are divided into three groups: osteoblastic, chondroblastic and fibroblastic, according to the dominant histologic feature. Osteosarcomas can be multifocal, synchronous or metachronous; they are also classified by the histologic grade of malignancy. Pathologically low grade lesions, which are clinically indolent, are generally known as low grade central and parosteal osteosarcomas.