[89] Morphologic and Immunohistochemical Characterization of a Series of Clinically Atypical Skull Base Chordomas in the Paediatric Population

CH Lee, NJ Liebsch, GP Nielsen, A Ganguly, AE Rosenberg. Vancouver General Hospital, Vancouver, BC, Canada; Massachusetts General Hospital, Boston, MA

Background: Chordomas are neoplasms that are hypothesized to arise from prexisting notochordal proliferations. While it is primarily a disease of adults, a subset of chordomas appears during childhood. These paediatric chordomas tend to occur in the skull base and a minority display unusually aggressive clinical behaviour with a propensity for metastases.
Design: We retrospectively examined a series of 22 paediatric chordomas that exhibited unusual pattern of disease progression including the presence of aggressive local growth and/or development of distant metastases. The aim is of the study is to identify specific histologic and immunohistochemical features that are common to this group of clinically atypical chordomas.
Results: The median age of the patients was 5.5 year (1 to 17 year). All of the primary tumors were located in the skull base region. Upon review, 17 of the 22 tumors demonstrated a morphologic appearance and/or immunohistochemical profile (positive for keratin and brachyury) consistent with chordoma, while the 5 remaining cases were poorly differentiated epithelioid neoplasms that strongly expressed keratin but lacked staining for brachyury. Of the 17 review-confirmed chordomas, only 3 chordomas displayed conventional morphology, while the majority (12 of 17 chordomas) showed increased cellularity in a large portion of the tumor (cellular variant). One remaining case showed focal dedifferentiation. A collagenous/demoplastic-type stromal background was seen in nearly half of these cases. Six of the 8 chordomas with positive Ki-67 stains showed a high proliferation index (> 10%) across multiple high power fields.
Conclusions: We have identified several important histologic features including increased cellularity, demoplastic-type stroma, and high proliferation index that are commonly encountered in clinically aggressive paediatric chordomas. Additionally, we found a small subset of poorly differentiated keratin-expressing and brachyury negative epithelioid neoplasms of the skull base that warrant more detailed characterization.
Category: Bone & Soft Tissue

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 18, Tuesday Morning


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