Kelley Liao

 Introduction: Colorectal cancer (CRC) is the second leading cause of cancer related deaths in the US. Cancer stem cells (CSC) are widely understood to be drivers of tumor progression and thus play an important role in the metastasis and development of CRC.¹ LGR5, a seven-transmembrane domain G protein-coupled receptor that participates in upregulating the WNT pathway, is an important molecular marker used for characterizing colorectal CSCs.^2,3 Despite its importance as a biomarker for CRC, the role of LGR5 has not been completely elucidated.² Characterizing the distribution of LGR5 within CRC adenomas could make it an invaluable cancer maker and potential therapeutic target. Methods: An organoid repository of adenomas from patients as well as samples from normal colon tissue was analyzed by immunohistochemistry and fluorescent activated cell sorting for presence of LGR5. LGR5(+) cells were then isolated and analyzed using RNA sequencing to colorectal cancer specific genes.⁴ Additionally, in-situ hybridization was carried out on human FFPE hyperplastic polyps, adenomas, and adenocarcinomas of all stages of CRC.^5,6 Results: The results of immunohistochemistry and fluorescent activated cell sorting demonstrated high concordance between LGR5(+) cells and genes associated with high levels of Wnt signaling, suggesting upregulation of Wnt pathway in CRC.⁴ Results of the in-situ hybridization carried out on polyps and adenomas revealed that in serrated adenomas, which represents a form of adenoma architecture that reflects 10-20% of CRC cases and is a non-APC mutant variety, LGR5 is localized to the basal crypts. The non- APC mutant form of CRC is  a less common mutation in CRC cancer in which APC has not undergone inactivation and can therefore act as a negative regulator of β-catenin within the Wnt pathway. There is a lack of LGR5 localization in conventional adenomas, which represent the majority of CRC cases (80-90%) and are of the APC mutant variety.⁵ Furthermore, LGR5 expression declines towards the invasive front of budding cancer cells. LGR5 suppression in the invasive front suggests that Wnt signaling is unlikely an associated mechanism at the budding front of adenomas.⁶ Conclusions: Heterogeneities of LGR5 distribution in CRC adenomas, such as decreased LGR5 at invasive tumor fronts and localization of LGR5 to basal crypts, may reflect different extents of Wnt signaling. Furthermore, the importance of characterizing differential distributions of LGR5 in CRC tissue has implications for basal crypts as a region of increased Wnt signaling and potential target for LGR5 specific therapies.

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