Chemosensitivity and stratification by a five monoclonal antibody IHC test in the NSABP B20 trial. Poster at ASCO 2007

Ross DT¹, Kim C², Tang G², Mejia OM², Beck RA³, Ring BZ¹, Seitz RS³, Paik S², Constantino JP⁴, and Wolmark N.^5
1Applied Genomics Inc., Burlingame CA, USA; ²National Surgical Adjuvant Breast and Bowel Project, Pittsburgh PA; ³Applied Genomics Inc., Huntsville, AL, USA; ⁴Dept of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA; ⁵NSABP and Allegheny General Hospital, Pittsburgh, PA;

Abstract

Background: We previously reported the association between a five monoclonal antibody test staining p53, NDRG1, SLC7A5, CEACAM5 and HTF9C and recurrence-free interval (RFI) in 711 ER+ N- breast cancer patients from Tamoxifen (Tam) arm of the NSABP trials B14 and B20 (SABCS 2006). In this study, we examined interaction between the test and chemotherapy in the B20 trial.

Subjects and Methods: Tissue array sections from B20 paraffin blocks were stained using standard IHC protocols (N=457). Predefined scoring rules and cut-points were applied. RFI was defined as time from entry to any local, regional or distant recurrence. Log-rank test was applied to assess the effect of chemotherapy for each risk stratum pre-defined by this IHC test. Interaction between risk strata and treatment was assessed by the likelihood ratio test in a Cox model with age and clinical tumor size adjusted.

Results: The IHC test identified high and low risk groups that both showed significant improvement upon treatment with cytotoxic chemotherapy.

Conclusion: It appears that five monoclonal antibodies may be able to identify groups of ER+, node negative patients who have greater absolute benefit from adjuvant Chemo compared to unstratified patient populations. However, the formal test for interaction between Chemo and the risk group was not significant (p-value=0.127). This may be due to small sample size and a lack of statistical power, or non-linearity of the test.

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