ER, PR, and HER2 assessment in Hispanic women with breast cancer: A comparison between IHC and AQUA technology.

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e11568 Background: Estrogen (ER), progesterone (PR) receptors and HER2 are important markers for breast cancer (BC) treatment planning. These markers are often measured by immunochemistry (IHC) but IHC is subject to limitations of operator subjectivity and equivocal results making selection of appropriate therapy difficult and ultimately affecting patient outcome. Methods: 135 females with BC were recruited in Puerto Rico between Sept and Dec 2012. Median patient age was 57 and 95 % had invasive ductal carcinoma. Our aim was to compare discordance rates of ER, PR and HER2 between IHC and AQUA, an automated fluorescent technology that quantifies antigen expression, in a population of Hispanic women and to investigate whether specimen type or tumor grade influence discordance rate between the two technologies. Results: 103 of 135 patient samples were found to be ER+ by both technologies and 28 samples were ER- by both IHC and AQUA. 4 samples (3%) were discordant; 2 each were AQUA+/IHC- and AQUA-/IHC+. 73 of 135 samples expressed PR by both technologies and 55 samples were PR- by both IHC and AQUA. 14 samples (10%) were discordant; 7 each were AQUA+/IHC- and AQUA-/IHC+. 87 of 135 samples were HER2- and 13 patients were found to be HER2+ by both technologies. However 35 samples (26%) were discordant for HER2 status; 31 were AQUA+/IHC- while 4 AQUA-/IHC+. 100 of the HER2 results were scored 0-1 (negative) by IHC and 25 % of these cases were overturned by AQUA to HER2 +. 19 of the HER2 results were scored 2 (borderline) by IHC. 32 % of these cases were positive by AQUA. Conclusions: Discordance rate were 3% for ER, 10 % for PR but 26% for HER2 between IHC and AQUA. The Cohen’s Kappa coefficient for ER and PR were 0.914 and 0.785 respectively but only 0.299 for HER2 (p values < 0.00001 for all 3 values). Needle/core biopsy yielded more HER2 discordance than lumpectomy/mastectomy (31% vs. 16%). HER2 discordance between IHC and AQUA was more common in higher grade tumors. The large number of HER2 negative IHC cases scored positive by AQUA, and considering the data demonstrating that HER2 by AQUA better predicts benefit from trastuzumab (Slamon D, SABCS 2012) suggests that a significant additional number of patients could benefit from such targeted therapy.

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