BackgroundAPC c.3920T>A; p.Ile1307Lys (I1307K), prevalent in individuals of Ashkenazi Jewish (AJ) origin, has been associated with a modestly increased colorectal cancer (CRC) risk. Clinical recommendations for I1307K heterozygotes vary across countries and expert groups, reflecting differences in population frequencies, modest risk estimates and limited data in non-AJ individuals.MethodsWe analysed UK Biobank data comprising 466 315 individuals (8944 with CRC), using genomic analysis to classify AJ and non-AJ ancestries.ResultsI1307K was identified in 7.1% of AJ and 0.08% of non-AJ white participants. No significant association with CRC was observed in AJ (OR: 0.71; 95% CI: 0.17 to 2.95) or non-AJ white individuals (OR: 1.05; 95% CI: 0.50 to 2.22). The previously established OR of 1.7-1.8 for AJ individuals lies within our 95% CI, indicating underpowered results due to limited CRC cases. No significant associations were detected for other cancers. Unbiased, adequately powered CRC case-control studies in non-AJ populations would require cohorts far larger than current resources for feasible analysis.ConclusionClinical actionability of I1307K should prioritise risk stratification based on overall CRC risk and ancestry-dependent variant detection rates. However, management strategies need not differ by ancestry once a carrier is identified, as the biological impact of I1307K should be consistent across populations.