Background

Various murine models have been developed to facilitate studies of human cancers and allow better understanding of mechanisms contributing to tumor growth. While heterotopic xenograft models involve implanting cancer cells into the flank of immunocompromised mouse subcutaneously, orthotopic tumor models more closely resemble the original tumor development due to the implantation of tumor cells directly into the organ of origin (Richmond and Su, 2008). Although orthotopic xenograft models are technically challenging and labor-intensive, orthotopic transplants are able to more accurately mimic human tumor and better predict a patient’s response to chemotherapy in comparison with heterotopic transplants because of the effects of tumor microenvironment (Talmadge et al., 2007). With increased knowledge regarding the important role of tumor-host cell interaction during tumor progression, genetically engineered mouse (GEM) models using immunocompetent mice extend our ability to model the complexity of human cancers (Gopinathan and Tuveson, 2008; Zitvogel et al., 2016). However, GEM models are more expensive, often require months to a year to develop tumors, and have the drawbacks regarding the heterogeneity of tumor frequency, latency and growth. By contrast, xenografts are less expensive, require less time to establish tumors, and have better reproducibility (Vandamme, 2014). In this protocol, we describe the procedure of generating orthotopic colorectal cancer by injecting human cancer cells into immunocompromised mice (Tseng et al., 2007; Liao et al., 2015).