[104] Parachordoma Involving Soft Tissue and Bone: A Distinctive Subgroup of Myoepithelioma or Extra-Axial Chordoma?

P Rao, AG Ayala, JM Meis. MD Anderson Cancer Center, Houston, TX; Methodist Hospital, Houston, TX

Background: Parachordoma is a rare bone and soft tissue tumor of uncertain lineage that occurs in non-axial locations. Although it was described several decades ago it remains enigmatic.
Design: We retrieved 16 cases from our archives using the search terms “parachordoma” and “soft tissue myoepithelioma”. Criteria for inclusion in the study included close morphologic resemblance to axial chordoma in the absence of known chordoma or carcinoma; 8 cases fulfilled these criteria. Immunohistochemical stains were performed. Corresponding clinical information was tabulated.
Results: Clinical data, available in 6/8 cases, showed there were 4 males and 2 females ranging from 12 to 67 years of age (median 42 years). All 8 cases involved the extremities specifically the deep soft tissues of the fingers, hand, forearm, foot or limb girdle with concomitant bone involvement in 6 cases; several appeared to be periosteal. The histologic appearance was uniform between cases & distinctive. All tumors had a lobulated growth pattern with a prominent chondroid to focally osseous matrix. Constituent cells, arranged in clusters or singly, were epithelioid with abundant eosinophilic to clear cytoplasm and variable nuclear pleomorphism. Focal necrosis was noted in 1 case. None demonstrated clear ducts, prominent spindle cells or plasmacytoid cells. Immunohistochemical stains showed 5/6 cases were positive for pancytokeratin, 4/6 for S-100 protein, 2/4 for p63 and 5/5 for SOX-9. 2 patients had metastasis: 1 to regional lymph nodes & the other to lung.
Conclusions: 1) Parachordoma involving soft tissue & bone has a striking predilection for the extremities & frequently involves the bone and soft tissue simultaneously. 2) It is locally aggressive & may metastasize. 3) It is histologically similar to chordoma. 4) The histologic differential diagnosis includes myoepithelioma, chondroid lipoma, extraskeletal myxoid chondrosarcoma, ossifying fibromyxoid tumor of soft parts, matrix producing breast carcinoma & metastatic chordoma. 5) The majority of parachordomas express keratin and S-100 protein as is seen in axial chordoma. It also demonstrates nuclear expression of SOX-9. 6) Clinical & histological features of parachordoma lend strong support to the concept that “parachordoma”, as defined in this study, is closely related to notochordal derived tumors (axial chordoma). 7) The intimate association of parachordomas with bone and soft tissue raises the possibility that periosteum/synovium may be the site of origin for this tumor.
Category: Bone & Soft Tissue

Tuesday, March 23, 2010 1:15 PM

Platform Session: Section E, Tuesday Afternoon


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