Abstract 3864: A transition zone showing highly discontinuous or rapidly oscillating levels of stem cell and proliferation markers characterizes the development of colorectal cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Stepwise acquisition of genetic changes characterize the development of colorectal cancer (CRC). These mutational events are correlated with discrete morphologic transitions from hyperplastic to adenomatous areas followed by in situ transformation and finally invasive carcinoma. The genetic drivers for each stage of this process, however, have not been fully established and can be confounded by tumor heterogeneity. The goal of this study was to identify easily assessed biomarkers of key morphogenetic transitions in CRC. Methods and Findings: We analyzed the pattern of proliferation and expression of growth regulatory and stem cell markers across distinct morphologic transition zones in 726 cases of CRC. In cases with preserved adenoma-carcinoma morphologic transitions, we identified a characteristic zone of adenomatous epithelium, often located immediately adjacent to and extending into the invasive component, that showed rapidly oscillating intraglandular stretches of Ki-67+ and Ki-67- cells. This pattern correlated with oscillating expression of other cell cycle mediators and the growth regulators PTEN and SMAD4. These multifocal stretches of adenomatous epithelium showed alternating abrupt positive/negative expression boundaries. These zones also demonstrated similar abrupt intragland oscillations in the levels and/or subcellular localization of multiple cancer stem cell (CSC) markers including beta-catenin/CTNNB1, MGMT and CD44. In contrast, the expression levels of most of these markers were largely homogenous in the proximal adenomatous and deeper invasive carcinoma surrounding the transitional region. This CSC-like transitional zone, as detected by PTEN IHC, was prominent in 50/726 of all CRC (6.9%) but at least focally present in 97/201 (48.2%) cases with intact adenoma-carcinoma junctions. Genomic microarray (OncoScan HD) and mutation analysis (Ampliseq) on CRC with prominent CSC-like expansions demonstrated complex genomic changes in 12/18 (66.7%) with a similar frequency of KRAS, BRAF and CTNNB1 mutations as expected in unselected CRC cases. The transition zones in these cases also frequently demonstrated unstable genomes from cell-to-cell (as assessed by FISH) indicating high genetic instability in these areas. Conclusions: We show that multiple immunohistochemical markers, including PTEN, SMAD4, CD44 and CTNNB1, highlight a localized CSC-like transition zone of rapidly alternating quiescent/proliferative adenomatous epithelium in primary CRC tumors. This transition zone often begins in pre-invasive adenomatous epithelium adjacent to invasive tumor areas that have more uniform proliferation and more homogeneous genetic and expression profiles. This easily assessed phenomenon appears to represent a commonly occurring genetically unstable forerunner or transitional stage in CRC evolution. Citation Format: Kevin J. Arvai, Ya-Hsuan Hsu, Lobin A. Lee, Dan Jones. A transition zone showing highly discontinuous or rapidly oscillating levels of stem cell and proliferation markers characterizes the development of colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3864. doi:10.1158/1538-7445.AM2014-3864