Correlation between the progesterone receptor isoform ratio determined in breast cancer biopsy cores and surgical samples

ELIA A; GONZALEZ P; BURRUCHAGA J; LIGUORI M; MARTINEZ VAZQUEZ P; LANARI C.; ROJAS P; CAILLET BOIS I; GASS H

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Seventy percent of breast cancers are susceptible to endocrine therapy currently aimed to target the estrogen receptor alpha (ERα). We have recently shown that breast cancer tissue cultures with higher levels of progesterone receptor (PR) isoform A (PRA) than isoform B (PRB) were inhibited by mifepristone whereas different responses were observed in those with the opposite ratio. This highlights the relevance of determining the PR isoform ratio to identify patients that may benefit from this therapy. The aim of this study was to evaluate the correlation between the PRA/PRB ratio determined by western blots (WB) in core biopsies and those determined in surgical samples from the same breast cancer patients from the Hospital ?Magdalena V Martínez? from General Pacheco (n=20). A similar trucut core was used for diagnostic purposes. The protocol has been approved by Institutional Review Boards. We determined the PRA/PRB ratio by WB using nuclear extracts from frozen tissues (biopsy and surgery) and the percentage of cells expressing PR, evaluated by immunohistochemistry (IHC), was obtained from the clinic records (surgical samples).WB and IHC data, regarding total PR expression, both obtained from surgical samples, were coincident in 90% of the cases. The few ones that differed, were samples in which the PR value determined by IHC was less than 20 % and the WB gave negative results. If the analysis is performed considering the WB data obtained from biopsy samples, the percentage decreases to 65 %, probably due to scant tumor cells in some biopsy cores. When the PRA/PRB ratios were compared between biopsy and surgical samples considering all cases in which WB biopsy data matched with the IHC data obtained in surgery, a 95% of coincidence was foundWe conclude the PR isoform ratio in biopsy cores reflects the PRA/PRB ratio in the tumors in cases in which PR values are higher than 20%. We are still recruiting patients to confirm this data in a larger cohort.