A balanced t(5;17) (p15;q22-23) in chondroblastoma: frequency of the re-arrangement and analysis of the candidate genes

Abstract

Background: Chondroblastoma is a benign cartilaginous tumour of bone that predominantly affects the epiphysis of long bones in young males. No recurrent chromosomal re-arrangements have so far been observed.

Methods: We identified an index case with a balanced translocation by Combined Binary Ratio-Fluorescent in situ Hybridisation (COBRA-FISH) karyotyping followed by breakpoint FISH mapping and array-Comparative Genomic Hybridisation (aCGH). Candidate region re-arrangement and candidate gene expression were subsequently investigated by interphase FISH and immunohistochemistry in another 14 cases.

Results: A balanced t(5;17)(p15;q22-23) was identified. In the index case, interphase FISH showed that the translocation was present only in mononucleated cells and was absent in the characteristic multinucleated giant cells. The t(5;17) translocation was not observed in the other cases studied. The breakpoint in 5p15 occurred close to the steroid reductase 5alpha1 (SRD5A1) gene. Expression of the protein was found in all cases tested. Similar expression was found for the sex steroid signalling-related molecules oestrogen receptor alpha and aromatase, while androgen receptors were only found in isolated cells in a few cases. The breakpoint in 17q22-23 was upstream of the carbonic anhydrase x (CA10) gene region and possibly involved gene-regulatory elements, which was indicated by the lack of CA10 protein expression in the index case. All other cases showed variable levels of CA10 expression, with low expression in three cases.

Conclusion: We report a novel t(5;17)(p15;q22-23) translocation in chondroblastoma without involvement of any of the two chromosomal regions in other cases studied. Our results indicate that the characteristic multinucleated giant cells in chondroblastoma do not have the same clonal origin as the mononuclear population, as they do not harbour the same translocation. We therefore hypothesise that they might be either reactive or originate from a distinct neoplastic clone, although the occurrence of two distinct clones is unlikely. Impairment of the CA10 gene might be pathogenetically relevant, as low expression was found in four cases. Diffuse expression of SRD5A1 and sex steroid signalling-related molecules confirms their role in neoplastic chondrogenesis.

Figure 1

From identification of an index case to frequency of the re-arrangement and analysis of the candidate genes: A) COBRA-FISH molecular karyotypes on metaphases from CB13 shows translocation between the short arm of chromosome 5 (white arrows) and the long arm of chromosome 17 (white arrows) (a schematic view of the rearrangement is given in the inset). B) The schematic view recapitulating the results of the FISH mapping (left) (chromosome 5 in the upper part and chromosome 17 in the lower part) The probes that resulted translocated are shown in red, and the retained ones are shown in green. On the right (from top to bottom), interphase FISH shows splitting of the probes covering chromosomes 5 (top) and 17 (bottom) breakpoint regions in the mononuclear cells of CB13, while no rearrangement was found in multinuclear giant cells (middle: confocal microscopy shows a giant cell with 2 nuclei with a normal paired red and green signal). C) Diffuse expression was found by immunohistochemistry for SRD5A1 (picture from CB13). Immunohistochemistry for carbonic anhydrase-related protein X is shown: absent signal in CB13 (D) and diffuse signal of moderate intensity in the other cases (E, CB11); heterogeneous staining was found in multinucleated giant cells. F) Scattered cells in matrix-rich areas were found to express AR (CB13). G) Heterogeneous staining was found in multinucleated giant cells for ESR1 (CB7) (magnification bar = 50 μm).