The associations between the CYP2C8/9 *1/*4/*1/*1 haplotype and CYP2C8/9 *3/*1/*2/*1 haplotypes and lymph node involvement was different depending on the invasive tumour size (exp(β)=0.33; Pinteraction=0.10 and exp(β)=3.2; Pinteraction=0.040, respectively, when entered into the same model). The gene discussed is CYP2C8; the disease is neoplasm.