Crook, Julia E.

Abstract Introduction: Invasive lobular carcinoma (ILC) comprises approximately ∼10-20% of breast cancers (BC) and appears to have a distinct biology from invasive ductal carcinoma (IDC). ILC is known to have a higher incidence of multifocal (MF) disease when compared to IDC (Biglia N, EJSO, 2013) and in general, MF BC has been associated with an increased rate of regional lymph node metastases (Cabioglu N, JACS, 2009). Treatment decisions are most often defined by the largest of the MF tumors without targeting potentially relevant biologic heterogeneity of the disease. We conducted a genomic analysis of MF ILC to help address this knowledge void. Methods: We characterized gene expression in multiple foci from 11 patients (pts) with MF ILC (all ER+ and HER2-, mean number of foci = 2.62) and 13 benign breast tissues. RNA was extracted from 3×1.5mm cores from each foci and gene expression was measured in 730 known cancer genes using the NanoString PanCancer pathways panel. Differential gene expression analyses were performed between 1) MF tumors and benign tissue (BT) accounting for pairing of pts and 2) different foci of MF tumors from the same ILC pt by ANOVA. The association of clinical covariates (age, number of tumors, grade and stage) in the top genes that were differentially expressed between multiple foci was assessed by linear mixed models accounting for pt and tumor. Results: A total of 20 genes (including MET and EGFR, top 5 genes: SPRY2, SOX17, FIGF, PDGFA, IL6) were differentially expressed (p<0.05) between malignant foci from the same pt, after correction by false discovery rate (FDR). EGFR expression was also negatively associated with the number of positive lymph nodes (N1a vs N0 absolute fold change = 0.51, p = 0.043). We observed an excess of genes that were down-regulated in MF ILC compared to BT. 277 genes were differentially expressed at p<0.05 after correction by FDR. The top 5 differentially expressed genes (by fold change) between ILC and BT were COL11A1, COL1A1, WIF1, FIGF and PROM1. CDH1, a known marker of ILC, was down-regulated in ILC compared to benign (absolute fold change = 2.54, p = 6.02×10−6), ranked only 39/277 genes by fold change. MET and EGFR ranked 29 and 42/277 genes (p = 5.99×10−9 and 3.32×10−8 respectively). Conclusion: We observed significant heterogeneity for 20/730 genes between individual foci of MF ILC within the same pt suggesting that MF synchronous ILC lesions may have different biologic behavior. This in turn may have important prognostic implications with potential therapeutic utility. Our analyses also shows significant down-regulation of gene expression between ILC tumors and BT for many genes other than CDH1 suggesting that additional biomarkers can be used to further characterize ILC Study funded in part by Mayo Clinic Cancer Focus Research Team, the 26.2 with Donna Foundation and the Serene M. and Frances C. Durling endowment. Citation Format: Pooja Advani, Nadine Norton, Daniel J. Serie, Xochiquetzal Geiger, Julia E. Crook, Aubrey E. Thompson, Edith A. Perez, Alvaro Moreno Aspitia. Characterization of individual foci of multifocal invasive lobular breast cancer using gene expression profiling. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4761. doi:10.1158/1538-7445.AM2015-4761