Abstract 4760: Evaluation of the progesterone receptor status using three different antibodies: A comparison by Allred score system.

Abstract

Abstract Abstract: Breast cancer (BC) hormonal receptors (progesterone, PgR and estrogen) status is assessed by immunohistochemistry (IHC), a specific, sensitive, and accessible method that guide BC treatment. We evaluated PgR expression in 53 BC cases using 3 anti-PgR antibodies (AB): monoclonal (SP42 and RP636) and polyclonal ab62621. Methods: Primary BC cases (with signed informed consent) were used to generate tissue microarray platforms, where PgR expression was accessed by IHC and evaluated by the Allred score. Categorical and quantitative data are shown in percentage and mean, respectively. Concordance (CON) and correlation among ABs were analyzed by Kappa factor (K), Spearman's correlation coefficient (ρ) or intraclass correlation coefficient. Staining patterns of each AB were compared by paired T-Test. Findings: We noted poor CON and K between ab62621 vs SP42 (CON=64.1%; K=0.247), and ab62621 vs RP636 (CON=62.3%; K=0.204), but higher CON between SP42 vs RP636 (CON 90.6%; K =0.738). Data were corroborated by Mc Nemar statistical test (p=0.019, p=0.014 and p>0.05, respectively). Regarding staining intensity among PgR+ samples, we found higher proportion of weak staining and lower IS for ab62621 (48.3%; mean IS=1.6), when compared to SP42 (20.0%, mean IS=2.1, T-test p<0.01) and RP636 (2.3, 21.9%, T-test p<0.01). Within the entire sample, similar results were observed following ρ: SP42 vs RP636 (ρ=0.8103); ab62621 vs SP42 (ρ=0.3524); ab62621 vs RP636 (ρ=0.4075). As for proportion of stained cells and PS, among PgR+ samples, the mean values for ab62621 (75.4%; 4.8) were significantly higher than those of SP42 (56.3%, 4.3; T-test p<0.01) and RP636 (60.1%; 4.2; T-test p<0.01). Similar data were found after analyzing PS for the entire sample: SP42 vs RP636 (ρ=0.8588); SP42 vs ab62621(ρ=0.4832); RP636 vs ab62621(ρ=0.4050). Interpretation: Our data indicate that anti-PgR monoclonal ABs, RP636 and SP42, are, unlike ab62621, equally suitable to test BC PgR status by IHC due to their higher accuracy. Therefore, we suggest their clinical use during BC diagnosis; thus, enabling more precise therapeutic decisions to treat BC. Citation Format: Klesia P. Madeira, Renata Daltoe, Alex Carvalho, Lucas Rezende, Ian Silva, Leticia Rangel. Evaluation of the progesterone receptor status using three different antibodies: A comparison by Allred score system. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4760. doi:10.1158/1538-7445.AM2013-4760 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.