[75] Loss of INI1 Expression in Extraskeletal Myxoid Chondrosarcoma

David L Stockman, Jason L Hornick, Wei-Lien Wang, Alexandar J Lazar. University of Texas MD Anderson Cancer Center, Houston, TX; Brigham and Women's Hospital, Boston, MA

Background: Extraskeletal myxoid chondrosarcomas (ESMC) are rare sarcomas of uncertain differentiation that often occur in the deep soft tissue of the lower extremity (LE) with metastases often detected during long-term follow up. Previously, INI1 loss was reported in a subset of ESMC. We investigated SMARCB1/INI1 expression by immunohistochemistry and examined for its prognostic significance.
Design: 18 cases of ESMC were retrieved. IHC was performed following antigen retrieval using a mouse anti-SMARCB1/INI1 antibody (1:50; BAF47; BD Biosciences). INI1 immunoreactivity was graded for extent (0, no staining; 1+, <10%; 2+, 10% to 25%; 3+, 26% to 50%; 4+, 51% to 89%; and 5+, 90% to 100%) and intensity (weak, moderate, strong). 0 to 3+ staining were considered to be loss of INI1 expression. All 18 cases were assessed by LSI EWSR1 dual-color, break-apart probe (Abbott Molecular/Vysis, Des Plaines, IL).
Results: Demographics were as follows: M:F ratio of 14:4 with median age of 54 yrs (range:29-79). ESMC cases involved the LE (9/18, 50%), arm and buttock (2/18 each, 11%), trunk (2/18, 11%), and metastatic sites (3/18). EWSR1 rearrangement was detected in 12/15 (80%) cases. 9 cases showed diffuse (5+ and 4+) strong labeling for INI1 while variable loss of INI1 expression was seen in 9/18 (50%) cases: 3 with or 3+ weak/moderate labeling, 3 with 1+ or 2+ weak labeling, and 3 with complete loss of expression. Clinical follow-up (F/U) was available in 17/18 pts (median: 83 mos; range: 38-274 mos). In pts whose tumors showed signficant INI1 loss (0-3+), 7/9 (78%) had metastatic disease (4 with had multiple); 3/9 (33%) were DOD with median overall survival (OS) of 57 mos (range: 41-79) and median disease-free survival (DFS) of 31 mos (range: 16-37); 6/9 (67%) were AWD with median F/U of 76 mos (range: 38-274) and median DFS of 39 mos (range: 7-227). Of the pts whose tumors showed complete INI1 retention, 7/8 (87.5%) were AWD with median F/U of 116 mos (range: 49-262) and median DFS of 57 mos (range: 1-243); 1/8 (12.5%) DOD (OS: 83 mos; DFS: 26 mos).
Conclusions: In this study, 50% of ESMC cases showed variable loss of INI1 expression. Patients whose tumors had loss of INI1 had lower OS and DFS. INI1 loss in ESMC may play a role in disease progression and may serve as a potential prognostic marker.
Category: Bone & Soft Tissue

Monday, March 4, 2013 1:00 PM

Poster Session II # 14, Monday Afternoon


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