MORPHOLOGICAL-CHARACTERISTICS OF CHONDROB LASTOMA - A RETROSPECTIVE INVESTIGATION OF 56 CASES FROM THE HAMBURG BONE-TUMOR REGISTRY

Representing only about 1% of all primary bone tumors, chondroblastoma constitutes a very rare bone tumor entity. 56 cases of chondroblastom a, that had been collected by the Hamburg Bone Tumor Registry from 197 2 to 1995, were examined histologically together with the radiological and clinical findings. In addition immunohistochemistry with antibodi es against S 100, PGM1, LCA and the proliferationmarker MIB 1 was perf ormed. The mean age was 20.4 years and male patients being the majorit y with a gender ratio of 2.7:1. Predominant localisation was the epiph yses of the long bones, although almost 40 % of the tumors were locate d at untypical sites. Usually a well-circumscribed lysis could be seen on plain X-Ray examination, however partial cortical destruction coul d be observed in one third of the cases. Histologically characteristic was a polygonal cell component with a weblike chonroid matrix, someti mes with a plane-like appearance. 5 cases showed a distinct nuclear po lymorphism making a distinction from osteosarcoma difficult. Using imm unohistochemistry all tumors except for one showed positive reaction f or S 100 protein. Although the histogenesis of chondroblastoma is not completely understood, morphological findings as well as the observed reactivity with the S 100 protein indicate the chondroid origin. No re activity for PGM 1 (CD 68) or LCA could be detected. All chondroblasto ma showed a low rate of proliferation, thereby being distinguishable f rom high malignant bone tumors. In general chondroblastoma show a beni gn biological behavior. Different behavior was observed in 2 cases. On e relapse located in the pelvis revealed local aggressive growth while in another case in the humerus a malignant transformation had taken p lace.