Toremifene, an Alternative Adjuvant Endocrine Therapy, Is Better Than Tamoxifen in Breast Cancer Patients with CYP2D6*10 Mutant Genotypes.

Purpose: Tamoxifen showed individual differences in efficacy under different CYP2D6*10 genotypes. Our study evaluated the prognosis of tamoxifen or toremifene in hormone receptor (HR)-positive breast cancer patients under different genotypes.

Materials And Methods: CYP2D6*10 genotypes of HR-positive breast cancer patients were determined by Sanger sequencing, and all the patients were divided into tamoxifen group or toremifene group.

Results: A total of 268 patients with HR-positive breast cancer were studied. The median follow-up time was 72.0 months (range, 5.0 to 88.0 months). Of these, 88 (32.9%), 114 (42.5%), and 66 (24.6%) patients had C/C, C/T, and T/T genotypes, respectively. Among patients who received tamoxifen (n=176), the 5-year disease-free survival (DFS) rate in patients with C/C and C/T genotype was better than that in patients with T/T genotype, and the difference was statistically significant (p < 0.001 and p=0.030, respectively). In patients receiving toremifene, CYP2D6*10 genotype was not significantly associated with DFS (p=0.325). Regardless of genotypes, the 5-year DFS rate was higher in patients treated with toremifene than in patients with tamoxifen (91.3% vs. 80.0%, p=0.011). Compared with tamoxifen, toremifene remained an independent prognostic marker of DFS in multivariate analysis (hazard ratio, 0.422; p=0.021). For all the 180 patients with CYP2D6*10 C/T and T/T genotypes, the 5-year DFS rate was significantly higher in the toremifene group than in the tamoxifen group (90.8% vs. 70.1%, p=0.003).

Conclusion: Toremifene may be an alternative adjuvant endocrine therapy for patients with CYP2D6*10 mutant genotypes.