Background: Colorectal cancer is the third most common cause of death in western countries. Anoikis, is a form of cell death induced by the loss of the contact to extracellular matrix. Resistance to anoikis has been reported to enable metastatic and invasive potential in malignant tumors. Therefore cell populations with anoikis resistance ability are crucial to be identified and targeted and yet so far only studied with anti-adhesion tests in vitro. Hence, we aimed at identifying and quantifying cell populations with anoikis resistance ability. Identification of these cell populations was based on recognition of cells with absence of both contact with the extracellular matrix and evidence of increased apoptosis rate.

Materials and methods: We used TMA material from a well characterized series of colorectal cancer patients (n=137) for identification and quantification of putative anoikis resistant (AR) subpopulations. We stained the specimens with hematoxylin and eosin and performed immunohistochemical stainings with antibodies to Ki-67 for proliferation rate, cleaved cytokeratin 18 (M30) for apoptosis rate, and for basement membrane (BM) proteins laminin and collagen IV. Carcinoma cell subpopulations with features of anoikis resistance were quantitated by using digital image analysis and their correlation with clinicopathological features and prognostic effect were analyzed.

Results: We identified micropapillary structures (MIPs;) presenting as focal piles of epithelial cells in columnar epithelium, cribriform and solid structures formed by carcinoma cells to be the subpopulations containing cells without ECM contact. All these three putative AR subpopulations showed lower apoptosis index as compared with other carcinoma cells. MIPs also presented with low PI. No clear association with clinicopathological features or KRAS or BRAF mutations were seen. Abundance of AR subpopulations was an independent prognostic factor and associated with a significantly worse patient survival.

Conclusion: Lower apoptosis rate in all three putative AR structures along with absence of basement membrane protein contact indicates ability of these cells to survive without matrix contact, i.e. anoikis is inhibited in them. Association of low apoptosis and proliferation rates in MIPs indicates this subpopulation being distinct to other putative AR subpopulations in cribriform and solid structures, and likely to represent a quiescent population. Our histopathological assay of anoikis resistance provides new prognostic information. More studies are needed to confirm these findings, to disclose the role of specific mutations in their pathogenesis, and to analyze whether their presence predicts responses to treatment modalities.

Citation Format: Madhura Patankar. Recognition of anoikis resistant subpopulation in colorectal carcinoma and their association to adverse prognosis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 346.