[1192] Frequent Immunohistochemical Expression of KIT in YWHAE-FAM22 Endometrial Stromal Sarcoma

Cheng-Han Lee, Lien N Hoang, Carolina Reyes, Rob A Soslow, Marisa R Nucci, Esther Oliva. University of British Columbia, Vancouver, Canada; Memorial Sloan-Kettering Cancer Center, New York, NY; Brigham and Women's Hospital, Boston, MA; Massachusetts General Hospital, Boston, MA

Background: Endometrial stroma sarcoma (ESS) with YWHAE-FAM22 genetic rearrangement is clinically more aggressive than ESS with JAZF1-SUZ12 genetic rearrangement and frequently shows extrauterine tumor extension at presentation. In addition to the high-grade round to epithelioid cell component that is invariably present, a subset of YWHAE-FAM22 ESS also contains an admixed low-grade fibrous spindle cell component. Its appearance in the round/epithelioid cell area can resemble that of gastrointestinal stromal tumor (GIST). The aim of this study is to characterize the immunohistochemical expression of two commonly used diagnostic markers for GIST - KIT and DOG1 in YWHAE-FAM22 ESS.
Design: The immunohistochemical expression of KIT (Dako, A4502) and DOG1 (Spring Bioscience, SP31) was examined using whole tissue sections of 12 YWHAE-FAM22 ESS. Membranous and/or cytoplasmic staining was evaluated, and the staining intensity was assessed (negative, weak, moderate and strong) relative to KIT and DOG1 positive GIST tumor.
Results: Of the 12 YWHAE-FAM22 ESS, 5 showed only high-grade round cell component, 2 showed only low-grade fibrous spindle cell component and 5 showed a mixture of the two components in the slides evaluated. The high-grade round cell component displayed moderate to strong membranous/cytoplasmic KIT staining in 10 of 10 cases (Figure 1). The low-grade spindle cell component showed weak cytoplasmic KIT staining in 2 of 7 cases and negative KIT staining in 5 of 7 cases. DOG1 staining was negative in all 12 cases examined, irrespective the components present.
Figure 1: An YWHAE-FAM22 ESS showing positive KIT staining in the high-grade round cell area of the tumor and negative staining in the adjacent myometrium.

Conclusions: The high-grade round cell component of YWHAE-FAM22 ESS consistently expresses KIT, with an intensity that is comparable to that seen in GIST. This represents a potential diagnostic pitfall in the evaluation of extrauterine YWHAE-FAM22 ESS tumor mass, particularly in situations where its uterine origin is not apparent.
Category: Gynecologic & Obstetrics

Tuesday, March 5, 2013 1:00 PM

Poster Session IV # 247, Tuesday Afternoon


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