Connective Tissue Oncology Society

2001 CTOS Annual Meeting Posters— Biology

CHROMOSOME 9 ALTERATIONS AND P16 EXPRESSION IN CENTRAL CHONDROSARCOMAS
J. V. Bovee¹, D. Federov¹, H. van Beerendonk¹, A. H. Taminiau⁴, R. Sciot², M. Debiec-Rychter³, A. M. Cleton-Jansen¹, P. C. Hogendoorn¹
¹Department of Pathology, Leiden University Medical Center, ²Department of Pathology, Leuven University, ³Center for Human Genetics, Leuven University, ⁴Department of Orthopedic Surgery, Leiden University Medical Center

OBJECTIVE: Chondrosarcomas are characterized by neoplastic growth of cartilage forming tumor cells. The majority (75%) arise centrally, in the medullar cavity, while a minority develop peripherally secondary to an osteochondroma. We previously investigated DNA-ploidy and loss of heterozygosity (LOH) at loci harboring the EXT-genes (implicated in hereditary multiple exostoses), the EXT-like genes, and at 9p21, 13q14, 17p13 and chromosome 10 in 12 central chondrosarcomas. Only 3 cases exhibited LOH, with 9p21 involved in all three. At 9p21 the p16 tumour suppressor gene is located. Our goal was to further investigate this chromosomal region and the expression of the candidate gene p16.

METHODS: LOH analysis was performed in the region of p16 on 38 additional cases. Cytogenetic analysis was performed on 16 central chondrosarcomas. p16 immunohistochemistry was performed on formalin-fixed paraffin-embedded tissue of 84 cases to estimate the effect of 9p21 alterations on p16 protein expression.

RESULTS: Of 38 central chondrosarcomas 12 (32%) revealed LOH in the 9p21 region. Seven central chondrosarcomas demonstrated an abnormal karyotype, 5 of which involved chromosome 9. Three central tumours showed involvement of the 9p12-22 region including t(9;10)(p22;q22), add(9)(p21) and add(9)(p12). For two of them paraffin blocks were available revealing absence of p16 protein expression. Two tumours with -9 and del(9)(q12) demonstrated p16 protein expression. In 3 chondrosarcomas demonstrating LOH at 9p21, p16 protein expression was absent, while in 6 out of 9 central chondrosarcomas without LOH at 9p21, p16 protein expression could be demonstrated. In general loss of expression of p16 by immunohistochemistry was found in 18 % of the cases.

CONCLUSION: The involvement of genes located at chromosome 9, especially the 9p12-22 region, is suggested both by the LOH results, p16 immunohistochemistry as well as the cytogenetic studies. Since 9p21 alterations are associated with the absence of p16 protein expression, this suggests an important role for the p16 tumour suppressor gene in the development of central chondrosarcomas.