Correlation of WT1 expression with tumor characteristics and clinical outcomes in mucinous breast carcinoma

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e22075 Background: Wilms' tumor 1(WT1) protein expression has been evaluated by immunohistochemistry (IHC) in various histologies of series of invasive breast carcinomas. It is overexpressed predominantly in the mucinous subtype, in both pure and mixed mucinous carcinoma. The objective of this study was to correlate WT1 expression with the clinical and biological features of mucinous breast carcinoma as well as with the clinical outcomes and management. Methods: A total of 83 cases of pure and mixed mucinous breast carcinoma diagnosed between January 1999 and May 2006 were selected from the Magee-Womens Hospital, University of Pittsburgh Medical Center pathology registry. WT1 expression was examined by IHC using tissue microarrays (TMA). Only nuclear staining for WT1 was counted. Patient age, tumor features, management, and clinical outcomes were recorded, and survival was documented at the last patient followup. Results: Median follow-up was 59m (13–158m). The vast majority of patients had strong expression of hormone receptors. Only 3 patients had HER2-positive tumors. Disease free survival (DFS) was 92%. Overall survival (OS) was 88%. Sixty four cases had sufficient tissue on TMA for WT1 expression. Among them, WT1 expression was identified in 21/33 (64%) of pure mucinous carcinomas and 9/31 (29%) of mixed type tumors. Patients in both WT1-positive and WT1-negative groups had similar rates of breast conserving surgery, adjuvant radiotherapy and endocrine therapies. However, patients in the WT1-positive group were older (median age 74 vs 55 years, p=0.02) and had smaller tumor (median tumor size 1.2 vs 1.75 cm, p=0.03) as compared to those in WT1-negative group. More patients with WT1-negative tumors received adjuvant chemotherapy (40.6% vs 13.8%, p=0.02). Although all the recurrences were observed in patients with WT1-negative tumors, there was no statistical association of DFS or OS with WT1 expression. Conclusions: Overall, both pure and mixed mucinous breast carcinomas have excellent prognosis. This retrospective study demonstrated that WT1 expression may be associated with favorable outcome/pathologic features for patients with mucinous breast carcinoma. Prospective clinical studies will help to further elucidate these findings. No significant financial relationships to disclose.