Tumor Biology In African-American Women With Breast Cancer Treated With Preoperative Chemotherapy: Lack Of Pathologic Complete Response Is Related To P53 Overexpression.

880 Background: African-American (AA) women with breast cancer have increased risk of death compared with white women. Biologic differences may contribute to outcome disparities for AA women. Our prior study demonstrates that AA women treated with preoperative (preop) chemotherapy have reduced pathologic complete response (pCR) rates compared to non-AAs. Methods: To further evaluate differences in tumor biology as a cause for this disparity, we examined tumor histology and markers on samples from women who received preoperative therapy, at the MBCCOP, Stroger Hospital of Cook County, in Chicago. Results: There were 21 AA (0% pCR) and 21 non-AA (19% pCR) women included. The number of women with grade 1, 2 or 3 tumors respectively was 2, 2 & 17 for AAs, and 0, 8 & 13 for non-AAs. Hormone receptor (HR) status was negative for 15 AAs and 11 non-AAs. HER2 overexpression was seen in 6 AAs and 7 non-AAs. Extra-capsular lymph node tumor extension was seen in 5 AAs and 7 non-AAs. Although AAs were more likely to have grade 3 tumors which were HR negative, these differences were not significant. Immunohistochemistry on paired samples for AAs from pre and post chemotherapy specimens, demonstrated mild decreases in HR and estrogen receptor beta immunostaining, and no change in epidermal growth factor receptor or p27 immunoreactivity. However, p53 immunoreactivity with both Pab1801 and D07 antibodies was increased in the post chemotherapy specimens. Conclusions: Higher tumor grade and HR negative status seen in AAs in our study, are more commonly associated with favorable response to preop therapy. However, pCR did not occur in these women. Mutant p53 may be associated with an unfavorable response to preop therapy, and the demonstrated increase in p53 overexpression in AAs in this study may be responsible for the observed lack of pCR. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration This research was funded in part by the NCI (MBCCOP Grant CA95867), Aventis Pharmaceuticals Inc. & the Avon Foundation