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Letrozole Compared With Tamoxifen As Initial Adjuvant Therapy for Breast Cancer

Department of Breast Medical Oncology, M.D. Anderson Cancer Center, Houston, TX

To the Editor:

It is excellent to see this updated report of the Breast International Group (BIG) 1-98 trial.¹ I agree with the authors that limiting the analysis to the two continuous therapy arms makes the results of the more mature data from the study much easier to interpret, as it removes the bias toward early events caused by the inclusion of the first 2 years' data from the sequential arms.

After the previous report and publication of this trial,² there was concern regarding highlighting of apparently nonsignificant subgroup data (particularly prior chemotherapy and nodal status). The emphasis on and conclusions drawn from these subgroup analyses were not appropriate, as clinical decisions should not be based on subgroup analyses without clear reasons for a differential treatment effect, confirmed with a significant interaction/heterogeneity test.³ The subgroup data in this updated report of BIG 1-98 confirm this view, and also highlight the risks of overinterpreting early subgroup analysis (26 months median follow-up in the case of the earlier BIG 1-98 data). I am in agreement with the authors of this 51-month update that there is no evidence that any of the subgroups demonstrate significantly greater relative efficacy for letrozole over tamoxifen.

I am also pleased that the authors have included the data on discontinuation of therapy, which was omitted from the previous report.² The BIG 1-98 and Arimidex, Tamoxifen, Alone or in Combination (ATAC) trials,^1,4 both of which study adjuvant treatment in newly diagnosed patients, demonstrate that there are fewer recurrences with the aromatase inhibitor than tamoxifen, although in BIG 1-98 there were more adverse events and withdrawals due to adverse events with letrozole than with tamoxifen, unlike ATAC where there were fewer with anastrozole than with tamoxifen.^1,4

AUTHOR'S DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

The author or immediate family members indicated a financial interest. No conflict exists for drugs or devices used in a study if they are not being evaluated as part of the investigation. For a detailed description of the disclosure categories, or for more information about ASCO's conflict of interest policy, please refer to the Author Disclosure Declaration and the Disclosures of Potential Conflicts of Interest section in Information for Contributors.

Employment: N/A Leadership: N/A Consultant: N/A Stock: N/A Honoraria: Aman U. Buzdar, AstraZeneca Research Funds: Aman U. Buzdar, AstraZeneca, Pfizer, Genentech, Taiho, Roche Testimony: N/A Other: N/A

ACKNOWLEDGMENTS

Aman U. Buzdar is the current chairman of Arimidex, Tamoxifen, Alone or in Combination Steering Committee.

REFERENCES

1. Coates AS, Keshaviah A, Thurlimann B, et al: Five years of letrozole compared with tamoxifen as initial adjuvant therapy for postmenopausal women with endocrine-responsive early breast cancer: Update of study BIG1-98. J Clin Oncol 25: 486-492, 2007[Abstract/Free Full Text]

2. The Breast International Group (BIG) 1-98 Collaborative Group: A comparison of letrozole and tamoxifen in postmenopausal women with early breast cancer. N Engl J Med 353: 2747-2757, 2005[Abstract/Free Full Text]

3. Buzdar AU, Baum M, Cuzick J: Letrozole or tamoxifen in early breast cancer. N Engl J Med 354: 1528-1530, 2005[CrossRef]

4. ATAC Trialists' Group: Results of the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial after completion of 5 years' adjuvant treatment for breast cancer. Lancet 365: 60-62, 2005[CrossRef][Medline]

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