Excellent outcomes with adjuvant toremifene or tamoxifen in early stage breast cancer

Fareston (toremifene) and tamoxifen, both selective estrogen receptor modulators, are therapeutically equivalent treatments for metastatic breast cancer. We hypothesized that toremifene as compared with tamoxifen given as adjuvant therapy for early stage breast cancer would result in equivalent survival with an improved side effect profile, therefore, providing superior therapeutic efficacy.

Subjects and methods. The North American Fareston versus Tamoxifen Adjuvant trial assigned 1813 perimenopausal or postmenopausal women with hormone receptor (HR) – positive invasive breast cancer to adjuvant treatment with either tamoxifen or toremifene. The primary outcomes evaluated were disease-free survival (DFS) and overall survival (OS).

Results. Median follow-up was 59 months. The baseline characteristics of the 2 treatment groups were well-balanced. On the basis of intenttotreat, 5-year actuarial DFS was not significantly different between tamoxifen and toremifene (91.2 % (standard error of the mean (SE) 1.2 %) vs 91.2 % (SE 1.1 %), respectively). Similarly, 5-year actuarial OS was not significantly different between tamoxifen and toremifene (92.7 % (SE 1.1 %) vs 93.7 % (SE 1.0 %), respectively). Controlling for patient age, tumor size, and tumor grade, a Cox multivariate survival analysis found no difference between patients randomized to toremifene versus tamoxifen in terms of OS (OR 0.951; 95 % confidence interval (CI), 0.623–1.451, p = 0.951) or DFS (OR 1.037; 95 % CI, 0.721–1.491, p = 0.846). Adverse events were similar in the 2 groups.

Conclusions. Women treated with adjuvant hormonal therapy enjoyed excellent DFS and OS. No significant differences were found between treatment with either tamoxifen or toremifene. Treatment of HR-positive patients with either tamoxifen or toremifene is appropriate.

1. Early Breast Cancer Trialists’ Collaborative Group (EBCTCG). Effects of chemotherapy and hormonal therapy for early breast cancer on recurrence and 15-year survival an overview of the randomized trials. Lancet 2005;365(9472):1687–717.

2. Osborne C.K. Tamoxifen in the treatment of breast cancer. N Engl J Med 1998;339(22): 1609–18.

3. Kallio S., Kangas L., Blanco G. et al. A new triphenylethylene compound, Fc-1157a. I. Hormonal effects. Cancer Chemother Pharmacol 1986;17(2): 103–8.

4. Gershanovich M., Garin A., Baltina D. et al. A phase III comparison of two toremifene doses to tamoxifen in postmenopausal women with advanced breast cancer. Eastern European Study Group. Breast Cancer Res Treat 1997;45(3):251–62.

5. Warri A.M., Huovinen R.L., Laine A.M. et al. Apoptosis in toremifene-induced growth inhibition of human breast cancer cells in vivo and in vitro. J Natl Cancer Inst 1993;85(17):1412–8.

6. Hirsimäki P., Aaltonen A., Mäntylä E. et al. Toxicity of antiestrogens. Breast J 2002;8(2):92–6.

7. White I.N. The tamoxifen dilemma. Carcinogenesis 1999;20(7):1153–60.

8. Hayes D.F., Van Zyl J.А., Hacking A. et al. Randomized comparison of tamoxifen and two separate doses of toremifene in postmenopausal patients with metastatic breast cancer. J Clin Oncol 1995;13(10):2556–66.

9. Valavaara R. Phase II trials with toremifene in advanced breast cancer: a review. Breast Cancer Res Treat 1990;16 Suppl:S31–5.

10. Krag D., Weaver D., Ashikaga T. et al. The sentinel node in breast cancer – a multicenter validation study. N Engl J Med 1998;339(14):941–6.

11. Kangas L., Nieminen A.L., Blanco G. et al. A new triphenylethylene compound, Fc-1157a. Cancer Chemother Pharmacol 1986;17(2):109–13.

12. Holli K., Valavaara R., Blanco G. et al. Safety and efficacy of a randomized trial comparing adjuvant torimefene and tamoxifen in postmenopausal patients with node-positive breast cancer. Finnish Breast Cancer Group. J Clin Oncol 2000;18(20):3487–94.

13. International Breast Cancer Study Group; Pagani O., Gelber S., Price K. Toremifene and tamoxifen are equally effective for early-stage breast cancer: First Results of International Breast Cancer Study Group Trials 12-93 and 14-93. Ann Oncol 2004;15(12):1749–59.

14. Pyrhonen S., Valavaara R., Modig H. et al. Comparison of toremifene and tamoxifen in post-menopausal patients with advanced breast cancer: a randomized double-blind, the ‘nordic’ phase III study. Br J Cancer 1997;76(2):270–7.

15. Milla-Santos A., Milla L., Rallo L., Solano V. Phase III randomized trial of toremifene vs tamoxifen in hormonodependant advanced breast cancer. Breast Cancer Res Treat 2001;65(2):119–24.

16. Tamoxifen for early breast cancer: an overview of the randomized trials. Early Breast Cancer Trialists’ Collaborative Group. Lancet 1998;351(9114):1451–67.

17. Jatoi I., Hilsenbeck S.G., Clark G.M., Osborne C.K. Significance of axillary lymph node metastasis in primary breast cancer. J Clin Oncol 1999;17(8):2334–40.

18. Nayfield S.G., Gorin M.B. Tamoxifenassociated eye disease. A review. J Clin Oncol 1996;14(3):1018–26.

19. Holli K.; Finnish Breast Cancer Group. Тamoxifen versus toremifene in the adjuvant treatment of breast cancer. Eur J Cancer 2002;38 Suppl 6:S37–8.

20. Carpenter R. Choosing early adjuvant therapy for postmenopausal women with hormone-sensitive breast cancer: Aromatase inhibitors versus tamoxifen. Eur J Surg Oncol 2008;34(7):746–55.

21. Perez E. Safety profiles of tamoxifen and the aromatase inhibitors in adjuvant therapy of hormone-responsive early breast cancer. Ann Oncol 2007;18 Suppl 8:viii26–35.

22. Desta Z., Ward B.A., Soukhova N.V.,Flockhart D.A. Comprehensive evaluation of tamoxifen sequential biotransformation by the human cytochrome P450 system in vitro: prominent roles for CYP3A and CYP2D6. J Pharmacol Exp Ther 2004;310(3): 1062–75.

23. Ingelman-Sundberg M. Genetic polymorphisms of cytochrome P450 2D6 (CYP2D6): clinical consequences, evolutionary aspects and functional diversity. Pharmacogenomics J 2005;5(1):6–13.

24. Goetz M.P., Knox S.K., Suman V.J. et al. The impact of cytochrome P450 2D6 metabolism in women receiving adjuvant tamoxifen. Breast Cancer Res Treat 2007;101(1):113–21.

25. Berthou F., Dreano Y., Belloc C. et al. Involvement of cytochrome P450 3A enzyme family in the major metabolic pathways of toremifene in human liver microsomes. Biochem Pharmacol 1994;47(10):1883–95.

26. Taras T.L., Wurz G.T., Linares G.R., DeGregorio M.W. Clinical pharmacokinetics of toremifene. Clin Pharmacokinet 2000;39(5):327–34.