Abstract P1-03-03: Invasive lobular carcinoma and invasive ductal carcinoma differ in immune response, translation efficiency and metabolic rate

Abstract

Abstract Background Invasive lobular carcinoma (ILC) is the second most common histological subtype of breast cancer after invasive ductal carcinoma (IDC). ILC differs from IDC in pathologic, molecular, and clinical features. ILC tumors are most often characterized as luminal A by PAM50 analysis, suggestive of an indolent disease. Yet, when matched for receptor status and tumor grade, patients with ILC tend to have worse long-term outcomes than patients with IDC. The main distinguishing molecular feature of ILC is the loss of functional E-cadherin, and yet, beyond that loss, the mechanisms underlying the differences between ILC and IDC are largely unknown. We examined the RNA expression profiles of ILC and IDC tumors to assess if there may be underlying vulnerabilities of ILC tumors to novel therapeutic strategies. Methods Differential expression analysis was performed on 159 luminal A (LumA) ILC tumors versus 311 LumA IDC tumors from The Cancer Genome Atlas (TCGA). The METABRIC cohort (65 LumA ILC and 533 LumA IDC) was used as a validation dataset. Pathway enrichment analysis was performed to identify potential differences in biological processes, and these potential differences were then tested in a series of in vitro experiments, using 3 ER+ ILC (MDA-MB-134VI, SUM44PE, and MDA-MB-330) and 3 ER+ IDC (MCF7, T47D, and ZR75.1) cell lines. Results Pathway analysis led to the identification of three main signaling differences between LumA ILC and LumA IDC: immune regulation, translation, and metabolism. A series of immune pathways, including Immunological Synapse, Biocarta IL17 pathway, and Response to Wounding were up-regulated in ILC tumors. We examined specific cell type markers, and found that ILC tumors have a higher activity of nearly all immune cell types, including CD4+ T cells, CD8+ T cells, B cells, NK cells, dendritic cells, M1 macrophages, and M2 macrophages. These results were surprising, since ILC tumors have a lower incidence of stromal inflammation, as defined by H&E staining, suggesting a unique immune regulatory mechanism in ILC. Next, we examined the translational regulation in ILC vs IDC tumors by comparing RNA expression and protein quantities as determined by RPPA analysis. ILC tumors have a lower protein:RNA ratio, suggesting a lower translation efficiency. This was reflected in the RPPA data by lower protein expression of eIF4G, ribosome protein S6 (S6) and p70-S6K in ILC tumors. Phosphorylation of 4E-BP1 (Ser65), eEF2, S6 (Ser235/236, Ser240/244), and mTOR (Ser2448) were also significantly lower in LumA ILCs. This lower translation efficiency was then validated in cell lines by O-propargyl-puromycin treatment. Finally, the pathway analysis suggested lower rates of metabolism in lobular tumors. Comparative studies of OXPHOS and glycolysis with a Seahorse analyzer confirmed this finding. Conclusions ILC tumors have a higher immune activity than IDC tumors, even with lower rates of stromal inflammation, suggesting a potential for differential response to immunotherapy. The lower rates of translation and metabolism, which are general identifiers of tumor dormancy, could enable ILC to escape from cytotoxic therapies, and may play an important role in the late recurrence of ILC. Citation Format: Levine KM, Du T, Zhu L, Tasdemir N, Lee AV, Van Houten B, Tseng GC, Oesterreich S. Invasive lobular carcinoma and invasive ductal carcinoma differ in immune response, translation efficiency and metabolic rate [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-03-03.