Using an Atomic Force Microscope (AFM) with a 5.3 um diameter spherical probe we determined the elastic modulus of human mammary epithelial cells (HMEC) as they undergo neoplastic transformation from normal to immortal, tumorigenic, and finally metastatic. We did the measurements over both cytoplasmic and nuclear regions; and as a function of the cells location with respect to a colony (inside a colony, on the periphery of a colony, isolated cells).Tumorigenic and metastatic cells will grow in multiple layers rather than as a colony when confluence increases. So our measurements do not include the inside of a colony part for tumorigenic and metastatic cells. Normal cells show a significant difference in modulus depending on their colony environment. Measurements to date indicate that the cytoplasmic moduli in these 3 different environments for normal HMEC cells are 220 +/- 40 Pa, 380 +/- 50 Pa, and 650 +/- 70 Pa respectively (modulus +/- sem). We expect to report moduli under similar conditions for immortalized and tumorigenic HMEC cells and metastatic cells known as MDA-MB-231. In addition, for normal HMEC cells, we observe moduli differences due to cellular structures with the nuclear modulus being significantly higher (280 +/- 30 Pa, 680 +/- 90 Pa, and 690 +/- 100 Pa respectively) than the modulus of the cytoplasm. We also plan to report on these structural differences for immortalized, tumorigenic and metastatic versions of HMEC cells.This work is supported by NSF Materials and Surface Engineering grant CMMI-1152781.