Minute Mesenchymal Chondrosarcoma within Osteochondroma: An Unexpected Diagnosis Confirmed by HEY1-NCOA2 Fusion

Publication date: Available online 26 March 2018
Source:Human Pathology
Author(s): Shunichi Toki, Toru Motoi, Mototaka Miyake, Eisuke Kobayashi, Akira Kawai, Akihiko Yoshida
Mesenchymal chondrosarcoma is rare and can be challenging to diagnose. Herein, we report a minute mesenchymal chondrosarcoma within an osteochondroma. A 12-year-old girl presented with an asymptomatic exophytic lesion of the rib. The tumor was clinically diagnosed as osteochondroma, and was excised after observation for 3years. The resected specimen revealed an unexpected minute (0.9cm) "monophasic" mesenchymal chondrosarcoma in the apex of the lesion. The sarcoma consisted of monomorphic spindle cells without hyaline cartilage. Fluorescence in situ hybridization detected NCOA2 rearrangement, and reverse transcription-polymerase chain reaction and sequencing detected a HEY1 (exon 4)-NCOA2 (exon 13) fusion transcript. The patient did not receive adjuvant therapy and is alive with no recurrence 6years after surgery. The present case highlights the value of careful pathological examination of specimens submitted as osteochondroma and emphasizes the usefulness of molecular assays in the diagnosis of mesenchymal chondrosarcoma in an atypical setting.



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