UGT1A6 and colorectal cancer: An ad hoc power calculation was performed in Quanto V1.2.4 (http://biostats.usc.edu/Quanto.html) using the outcomes observed in the current study to assess the number of cases and controls needed to carry out an interaction test between UGT1A6 SNP, aspirin only use and colorectal cancer risk with two-sided P value of 0.002 (corrected for multiple tests) and 80% power.