Five cases of dedifferentiated chondrosarcoma of bone are presented. Three women and two men of age ranging from 57–72 years (median 63 years) suffered from tumors located in femur (2), scapula (1), humerus (1) and pelvis (1). They were all bulky tumors destroying the bones and infiltrating into the adjacent soft tissues in maximum diameter from 5–20 cm (median 12 cm). Both the short clinical histories lasting from 2–24 months (median 5 months) and persistent pains unrelieved by acylpirin were constant findings in all the cases. Four patients died of metastatic disease (mainly to lungs) with median survival of 8 months. All cases were the so-called „de novo“ dedifferentiated chondrosarcomas without clinical or morphological evidence of the primarily benign or malignant chondroid lesions. The tumors displayed a typical dual composition with an abrupt interface between chondroid and nonchondroid components. The chondroid tissue resembled G1 chondrosarcoma in three cases, G2–3 chondrosarcoma in two cases. The second nonchondroid mesenchymal portion had the appearance of undifferentiated pleomorphic sarcoma in three cases, rhabdoid and giant cell tumor-like in one case. The new data and evidence provided by molecular biology dramatically changed the opinions of histogenesis of this unique neoplasm. At present, there is a generally accepted idea of common origin of both portions from a primitive stem cell. Therefore, this peculiar tumors should not be viewed merely as dedifferentiated conventional chondrosarcomas.

        Key words: skeleton – chondrosarcoma – dedifferentiated chondrosarcoma