Using novel protein antibodies on tissue microarrays (TMAs) for breast cancer prognostication

Abstract

9629 Background: Estrogen receptor (ER) and progesterone receptor (PR) are important prognostic and predictive factors for breast cancer patients (pts). Murine monoclonal antibodies (MuAb) are currently used in immunohistochemistry (IHC) assays to determine ER/PR status. Rabbit monoclonal antibodies (RAb) may have greater affinity for human antigens than MuAb. We compared the concordance of MuAb- and RAb-based IHC assays of ER and PR and the prognostic value of these and other factors in pts with Stage I-III breast cancer. Methods: TMAs were produced from formalin-fixed paraffin-embedded tissue sections of primary breast cancer pts. IHC assays were performed for the following: ER/PR status using RAb SP1CLONE (Labvision™) and using MuAb (Ventana™), fascin (a tumor cell motility protein) using clone 55K-2 (DAKO/M3567™), cytokeratin 5/6 (CK5/6) using clone D5/164B (Roche Biomed/1273396™), and HER2 using CB11. These were correlated with stage, progression-free (PFS) and overall survival (OS). ER/PR positivity was defined as ≥5% estimated proportion of positive-staining tumor cells. Results: 199 pts were evaluable for ER/PR. The concordance rate for RAb- and MuAb- assessed ER status was 90% (180/199). The level of agreement for RAb- and MuAb- assessed PR status was 81% (162/199). ER/PR positivity by RAb correlated with each other, HER2 negativity and earlier stage. In 159 pts with evaluable follow up, pts with ER positivity by RAb had better 5-year PFS (p<.001) and OS (p=.03), similar to ER positivity by MuAb. Pts with PR positivity by RAb had superior 5-year PFS (p=.001) and OS (p=.04) and correlated better with survival than PR positivity by MuAb. Fascin was expressed in 34 pts. Using univariate analysis, fascin expression correlated with higher stage, negative ER/PR, shorter PFS and OS. CK5/6 positivity did not correlate with any variable, except ER/PR positivity by RAb. After multivariate analysis, significant factors for PFS were stage, HER2, and PR by RAb, and for OS were stage, HER2, and fascin positivity. Conclusion: 1) The RAb for PR may be superior to the MuAb in predicting prognosis. 2) Fascin deserves further investigation as a prognostic factor. No significant financial relationships to disclose.