Primary spinal intradural mesenchymal chondrosarcoma with detection of fusion gene HEY1-NCOA2: A paediatric case report and review of the literature

Abstract

Mesenchymal chondrosarcoma is an extremely rare malignant tumour that most commonly originates in the bone, but is also present in extraskeletal sites. The tumour is morphologically characterized by a biphasic pattern of small round cells and islands of cartilage. Spinal mesenchymal chondrosarcomas are even rarer and, therefore, few investigations exist regarding the biological behaviour of the tumours. In the present study, we report a case of a 10-year-old female presenting with 9 months of back pain and radiographic findings of an intradural lesion measuring 1.5 cm at the level of Th4. The tumour was completely excised and subjected to pathological analyses. Following detection of the HEY1-NCOA2 fusion gene, the tumour was morphologically and immunohistochemically defined as an intradural mesenchymal chondrosarcoma attached to the dura mater. In this study, we validate the recent identification of the fusion gene HEY1-NCOA2 in paediatric extraskeletal mesenchymal chondrosarcomas. The relevant literature is reviewed and further discussed in relation to our findings.

Keywords: HEY1-NCOA2; bone tumour; chondrosarcoma; fusion gene; intradural; sarcoma.

Figure 1

(A and B) Typical morphological features of mesenchymal chondrosarcomas showing a biphasic pattern of cartilage islands distributed among spindle cells, mainly located in the periphery. Chondrocytes showed moderate nuclear atypia, while spindle cells exhibited nuclear hyperchromatism and pleomorphism [staining, haematoxylin and eosin; magnification, ×200 (A) and ×400 (B)]. (C) The proliferation index (Ki-67) was high in the spindle cell component, but low in the cartilage islands (magnification, ×200). (D) After staining for CD99 (MIC 2), strong immunoreactivity was observed only in the peripheral cellular part of the tumour (magnification, ×400).

Figure 2

RT-PCR results. Paraffin-embedded tumour tissue was used for the RT-PCR. RT-PCR with specific primers for HEY1-NCOA2 fusion gene showed a strong band of 119 bp. RT-PCR, reverse transcription-polymerase chain reaction.

Figure 3

Primers were derived from exon 4 of HEY1 and exon 13 of NCOA2. Following direct sequencing of the reverse transcription-polymerase chain reaction product, sequences were manually aligned with the original sequences of HEY1 (NM_012258.3) and NCOA2 (NM_006540.2).