Heterocyclic aromatic amines formed in cooked meat may be an underlying mechanism for the red meat-colorectal cancer (CRC) association. These compounds require bioactivaction by N-acetyltransferase 2 (NAT2). An interaction effect between red meat consumption and NAT2 in increasing CRC risk has been inconsistently reported in whites. We investigated this interaction in two populations in which the high-activity rapid NAT2 phenotype is 10- and 2-fold more common than in whites. We meta-analyzed four studies of Japanese (2,217 cases, 3,788 controls) and three studies of African Americans (527 cases, 4,527 controls). NAT2 phenotype was inferred from an optimized seven-SNP genotyping panel. Processed and total red meat intakes were associated with an increased CRC risk in Japanese and in both ethnic groups combined (P’s ≤ 0.002). We observed an interaction between processed meat intake and NAT2 in Japanese (P = 0.04), African Americans (P = 0.02), and in both groups combined (P = 0.006). The association of processed meat with CRC was strongest among individuals with the rapid NAT2 phenotype (combined analysis, OR for highest vs. lowest quartile: 1.62, 95% CI: 1.28–2.05; Ptrend = 8.0×10−5), intermediate among those with the intermediate NAT2 phenotype (1.29, 95% CI: 1.05–1.59; Ptrend = 0.05) and null among those with the slow phenotype (Ptrend = 0.45). A similar interaction was found for NAT2 and total red meat (Pinteraction = 0.03). Our findings support a role for NAT2 in modifying the association between red meat consumption and CRC in Japanese and African Americans
