Genetic instability in epithelial tissues compared to stromal tissues Genetic instability in epithelial tissues compared to stromal tissues. Data showing that human mammary fibroblasts (HMFs; left upper panel) undergo a limited number of cell divisions (phase a) before undergoing irreversible arrest, called senescence (phase b). In contrast, HMECs (upper right panel) exhibit an initial growth phase (phase a) that is followed by a transient growth plateau (termed selection or phase b), from which proliferative cells emerge to undergo further population doublings (phase c; approximately 20 to 70 doublings) before entering a second growth plateau (phase d). Seen in the panels below are representative cell images from each phase for each cell type. HMECs emerge from senescence, exhibit eroding telomeric sequences (see Sec. 5.6) and, ultimately, enter telomere-based crisis to generate the types of chromosomal abnormalities seen in the earliest lesions of breast cancer and point to differences between epithelial cells and fibroblasts during neoplastic transformation. (Data from Romanov et al, 2001.) Source: Genomic Stability and DNA Repair, The Basic Science of Oncology, 5e Citation: Tannock IF, Hill RP, Bristow RG, Harrington L. The Basic Science of Oncology, 5e; 2016 Available at: http://hemonc.mhmedical.com/DownloadImage.aspx?image=/data/Books/1791/tanbas5_Ach5_f002.png&sec=124303586&BookID=1791&ChapterSecID=124303573&imagename= Accessed: October 15, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved