Characterization of the tumor immune microenvironment (TIM) with multiplex immunohistochemistry (mIHC) in patients with breast cancer following treatment with MK-2206

e12109 Background: The PAM (PI3K/Akt/mTOR) signaling pathway has been implicated in the oncogenesis of multiple solid malignancies, including breast cancer (BC). Our aim is to characterize the TIM in a series of patients with operable stage I-III BC treated with MK-2206, an allosteric Akt inhibitor within a presurgical trial. In NCT01319539 , patients received 2 doses of MK-2206 with first dose at day -9 and second at day -2 from surgery. Methods: mIHC was performed using immune biomarkers (DAPI, CD3, CD8, CD4, FOXP3, CD68, Pancytokeratin) on full section (4uM) tissue slides from core biopsy specimens and postsurgical specimens of 10 patients - 5 treated with MK-2206, 5 paired controls. Images were taken using Vectra, a novel pathology workstation and analyzed using inForm software to perform cell classification and phenotyping. T- tests were used to compare biomarker changes before and after MK-2206. Results: Our preliminary analysis demonstrates that patients treated with MK-2206 exhibited an increase in median cytotoxic T-cells (CD3CD8+) density, as compared to the control population , which was statistically significant (87% vs.0.2%, p < 0.05). We did not identify a change in macrophage (CD68) or T helper/T reg (CD4/CD4FOXP3+) density following MK-2206 treatment in this small cohort. We are currently expanding our myeloid panel as well as performing additional tissue analysis to validate our findings. As data is exploratory no correction was made for multiple comparisons. Conclusions: Tumor infiltrating lymphocytes (TILs) are both prognostic of overall survival as well as predictive of response to neoadjuvant chemotherapy in BC. At present, there are currently both FDA approved therapies, as well as agents in clinical development that exert antineoplastic activity through the PAM pathway. Investigations that endeavour to understand the impact of these therapies on the tumor immune microenvironment may lead to both an increased understanding of the bioactivity of these agents and potentially identify aspects of the immune response which can be exploited in future therapeutics.