UGT1A1 and Lynch syndrome: Specifically, 23.0% (14/61) of individuals susceptible to HBOC were also CYP2D6 intermediate or poor metabolizers, who are at higher risk of therapeutic failure for tamoxifen and breast cancer recurrence, whereas eight among 17 individuals with Lynch syndrome predisposition carried either a UGT1A1*6 or UGT1A1*28 allele associated with toxicities related to irinotecan-based chemotherapy.