[Extraskeletal osteosarcoma: nosologocal diversity, morphology, differential diagnosis, and features of metastasis].

Extraskeletal osteosarcoma is a rare malignant tumor with histologic similarities to primary bone osteosarcoma. However, there are distinct differences in epidemiology, imaging features, biological characteristics, prognosis, and management compared with osteogenic osteosarcoma. Extraskeletal osteosarcoma is usually characterized as high-grade neoplasm with clinically aggressive behavior, poor prognosis, frequent recurrence/lymphogenic metastatsis, and resistence to chemotherapy. A noteworthy feature of extraskeletal osteosarcoma is the fact that almost all existing biological phenomena described in mesenchymal oncopathology (except primary-multiple lesions) are present in this tumor, namely: secondary malignancy, association with syndromes, partial spontaneous regression of the tumor, dedifferentiation, bone invasion, biphasic pathology. In this paper, we have discussed in detail the tumor morphology, histological subtypes, prognostic factors and differential diagnosis.