The differences between these classes of cells may derive from the division of Wnt-positive colorectal cancer cells into high-Wnt and low-Wnt cell fractions, with the former being more sensitive to the pro-apoptotic effects of butyrate 1,2; this would be consistent with a graded apoptotic response to the levels of Wnt activity and of inactivated Rb in given cells 63. This evidence concerns the gene RB1 and colorectal cancer.