Abstract P3-06-07: Alterations of intratumoral signalling in breast cancer patients receiving pre-operative trastuzumab alone or combined with everolimus
Authors: Merlin Jean-Louis , Lion Maeva , Wong Jennifer , Bachelot Thomas , Andre Fabrice , Treilleux Isabelle , Loussouarn Delphine , Bonneterre Jacques , Rios Maria , Dieras Véronique , Jimenez Marta , Leroux Agnès , Campone Mario 
Published: May 2015

Background: PI3K/AKT/mTOR and MAP kinase pathways are major signaling pathways involved in mammary tumorigenesis and are investigated as putative targets for therapy. Multiple cross-talks exists between these two pathways, allowing the regulation of one another by and inversely, depending on the cell conditions. It has been reported that trastuzumab acted differently when used pre-operatively or in neo-adjuvant setting with a lower implication of signaling blockade and a higher induction of ADCC when used alone in chemotherapy naive patients. Additionally, mTOR blockade has been experimentally reported to activate MAPK pathway through a feed-back loop effect. The purpose of this study was to retrospectively investigate the effect on MAPK signaling of adding everolimus to trastuzumab as preoperative therapy of HER-2 positive primary breast cancer amenable to surgery (Unicancer RADHER Phase II trial).

Patients and methods: Formalin-fixed paraffin embedded and frozen tumor samples of primary breast cancer (n=80), were obtained from 82 patients with infiltrating breast carcinoma randomized from July 2008 to April 2012 to receive ttrastuzumab alone (T arm) (loading dose 4mg/kg, then 2mg/kg/week), or combined with everolimus (T+E arm) (10 mg/day) for a 6 week pre-operative treatment. The median patient age at diagnosis (at the randomization) was 52.7 years. All patients had baseline biopsies taken before initiation of the treatment, at cycle 4 as an option and at surgery. FFPE samples were used for immunohistochemistry (pAKT, pS6K, eIF4E, LKB1), frozen samples were used for multiplex immunoanalysis of phosphorylated PI3K/AKT/mTOR and MAPKinase signaling proteins analysis (p-AKT, p-GSK3, p-P70S6K, p-MEK1, p-ERK1/2, p-P90RSK). Before being submitted to total protein extraction, all biopsies were controlled to ensure a tumor content &gt;50%. 40 pairs associating baseline + surgery tumor specimens or baseline + cycle 4 biopsies were eligible for protein extraction.

Results: No statistically significant relationship was observed between the expression level of any of the phosphoproteins in the initial biopsies and neither the clinical nor the pathological response, overall. After treatment, as compared to the level of expression measured in the initial biopsies, no significant variation of expression of either PI3 kinase or MAP kinase related phosphoprotein was observed in T arm. In T+E arm, significant inhibition of PI3 kinase/mTOR pathway was only observed downstream mTOR protein with decreased expression of p-P70S6 kinase and p-4EBP1 together with a significant activation of MAPK pathway was detected with increased expression of p-MEK1, p-ERK1/2 was observed in T+E arm.

Conclusion: These results confirm that when used alone in chemotherapy naive patients, trastuzumab could not mainly act through the blockade of signaling and therefore when combined with mTOR inhibitors could lead to the suppression of negative feedback regulation of MAP kinase pathway.

Citation Format: Jean-Louis Merlin, Maeva Lion, Jennifer Wong, Thomas Bachelot, Fabrice Andre, Isabelle Treilleux, Delphine Loussouarn, Jacques Bonneterre, Maria Rios, Véronique Dieras, Marta Jimenez, Agnès Leroux, Mario Campone. Alterations of intratumoral signalling in breast cancer patients receiving pre-operative trastuzumab alone or combined with everolimus [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-07.