We investigated if the undetectable internalization of endogenous CysLT1R in Caco-2 cells was due to a mutation in the endogenous receptor of colon cancer cells; the CysLT1R from three colon-cancer cell lines (Caco-2, SW-480, and HCT-116) were sequenced. The gene discussed is CYSLTR1; the disease is colonic neoplasm.