Abstract 4326: Tissue density can create a carcinogenic microenvironment for normal mammary epithelial cells
Authors: Nazari Shayan , Mukherjee Pinku 
Published: July 2017

Background Breast cancer is the most diagnosed cancer and the fourth leading cause of cancer related mortality among females. Mammographic density (MD) is defined by the amount of stromal and epithelial tissues present in the breast tissue. Fifty percent of women have high MD and are 4-6 times more likely to develop breast cancer in their lifetime compared to women with low MD. Additionally, mammograms often miss abnormal lesions in high MD breast leading to late-stage diagnosis. The stromal microenvironment is characterized by extracellular matrix (ECM) reorganization and stiffness, and increase in ECM proteins including collagen I and fibronectin, which drives proliferation, tumor cell survival and migration. Expression of fibronectin and collagen are significantly higher in women with high MD compared to women with low MD. However, the mechanisms underlying the initiation and progression of breast cancer associated with MD remains largely unknown. Therefore, understanding the molecular pathways involved in the unique transformation of normal mammary cells to cancer cells in a dense microenvironment is an important step in finding diagnostic tools and therapeutic targets for prevention and treatment of breast cancer.

We hypothesize that normal mammary epithelial cells behave like cancer cells in an ECM protein-rich microenvironment by activating pathways associated with tumor growth and survival and contributing to the initiation and progression of breast cancer.

Methods We conducted an in vitro study, determining the effects of different concentrations of ECM proteins on the activation of pro-carcinogenic pathways including the MAPK pathway and the PI3 Kinase pathway using Western blotting analysis. This study helps us understand if there is a difference in the expression of ERK1/2 signaling and/or PI3 Kinase signaling in normal mammary cells (hTERT) seeded on culture dish coated with ECM-proteins (collagen and fibronectin), compared to a non-coated control. We also examined morphological changes that can occur in a breast cancer cell line (HCC1806) that are seeded on ECM-rich coating dishes compared to non-coated dishes.

Results We observed changes in the morphology of breast cancer cell lines after cells were seeded on increasing concentration of extracellular matrix coatings using light microscopy. We also observed an increase in the expression of PI3 Kinase in normal mammary cell lines compared to control after cells were stressed using hypoxia.

Conclusion Collagen and fibronectin-rich microenvironment can induce desmoplastic-like phenotype and behavior for normal mammary cells, which highlights the possible first steps in transformation of normal mammary cells to desmoplastic cells. Given that high MD is one of the major risk factors for breast cancer development, it is critical to decipher the molecular mechanisms associated with the high risk.

Citation Format: Shayan Nazari, Pinku Mukherjee. Tissue density can create a carcinogenic microenvironment for normal mammary epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4326. doi:10.1158/1538-7445.AM2017-4326