[177] Immunoexpression of Fli-1 by Metaplastic Breast Cancer: A Potential Pitfall in Cases Morphologically Resembling Epithelioid Angiosarcoma

RM Gill, EF Brachtel, AE Horvai, YY Chen, JT Rabban. UCSF, San Francisco, CA; Massachusetts General Hospital, Boston, MA

Background: Metaplastic breast carcinoma may exhibit spindled or vasoformative morphology that resembles epithelioid angiosarcoma. This may cause particular diagnostic difficulty in core biopsies of the breast. Immunoexpression of epithelial markers can be demonstrated in many metaplastic breast cancers but also in a minority of epithelioid angiosarcoma. Immunoexpression of vascular markers (Fli-1, CD31, CD34) characterize angiosarcoma, but Fli-1 immunoexpression in metaplastic breast cancer has not been formally defined. In this study, we compare the diagnostic utility of Fli-1 immunoexpression to distinguish metaplastic breast cancer with angiosarcomatous features from epithelioid angiosarcoma.
Design: Formalin-fixed, paraffin-embedded tissue sections were selected from 14 metaplastic breast cancers that resembled angiosarcoma. Eleven cases of epithelioid angiosarcoma (from either soft tissue or breast origin) were selected for comparison. Immunostaining was performed for Fli-1 (BD Biosciences, 1:50), CD31 (Biogenex, 1:4), CD34 (Novocastra, 1:400), high molecular weight keratin (HMWK 903, Enzo, 1:2), Keratin MNF116 (DAKO, undiluted), and p63 (Labvision, 1:400). Nuclear expression of Fli-1 and p63 was defined as positive. Cytoplasmic or membrane expression of the remaining markers was defined as positive.
Results: The proportion of metaplastic breast cancers expressing Fli-1 (9/14, 64%) was not significantly different than Fli-1 expression by epithelioid angiosarcoma (10/11, 91%) (p = 0.16), however, the intensity and distribution of expression was markedly different. In metaplastic breast cancer, Fli-1 was weak and patchy in most cases whereas in all epithelioid angiosarcoma, Fli-1 was diffuse and intense. Keratins 903 and MNF-116 were expressed in 14/15 and 13/13 metaplastic breast cancers and in 3/11 and 3/11 epithelioid angiosarcomas, respectively. p63 was expressed in 6/9 metaplastic breast cancers and 2/11 epithelioid angiosarcomas. None of the metaplastic breast cancers expressed CD34 but in 2 cases CD31 was expressed in scattered rare tumor cells.
Conclusions: Although Fli-1 immunoexpression can be detected in metaplastic breast cancer, the staining intensity and distribution is minimal and should not be interpreted as evidence of epithelioid angiosarcoma. A broad panel of epithelial markers, p63, and other vascular markers should be used instead of relying on Fli-1 alone to diagnose angiosarcoma in the breast.
Category: Breast

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 24, Tuesday Afternoon