Beyond tamoxifen--extending endocrine treatment for early-stage breast cancer

Correlation of changes between 2-year disease-free survival and 5-year overall survival in adjuvant breast cancer trials from 1966 to 2006

BACKGROUND

Although disease-free survival (DFS) is accepted as a valid end point in adjuvant breast cancer trials, improvement in 2-year DFS has never been formally established as an adequate correlate for 5-year overall survival (OS). We set out to ascertain if changes in 2-year DFS can be used to accurately predict 5-year OS changes.

DESIGN

We conducted a systematic Medline search (1966-2006) for randomized adjuvant breast cancer trials of >100 patients per arm with 2-year DFS and 5-year OS data. A univariate regression model weighted by trial sample size was constructed to determine whether 2-year DFS differences between treatment arms within trials were predictive of 5-year OS differences.

RESULTS

A total of 126 studies containing 149 treatment comparisons met the inclusion criteria. Difference in 2-year DFS was a significant predictor of difference in 5-year OS. For every 1% increase in 2-year DFS difference, the 5-year OS difference increased by 0.5%-0.55%. The proportion of variation explained ranged from 0.38 to 0.42, with a wide prediction interval.

CONCLUSION

There is a statistically significant correlation, of moderate strength, between difference in 2-year DFS between treatment comparisons and difference in 5-year OS but the correlation is not strong enough to be used as a predictor.

Aromatase Inhibitor Agents in Breast Cancer: Evolving Practices in Hormonal Therapy Treatment

PURPOSE/OBJECTIVES

To review the role of aromatase inhibitor agents with regard to current treatment strategies with hormonal therapy for women with breast cancer.

DATA SOURCES

Published articles and books.

DATA SYNTHESIS

Hormonal therapy is an essential component of the treatment of most women with breast cancer. Aromatase inhibitor agents are becoming an integral part of treatment for women with metastatic breast cancer and recently have become much more prominent in the treatment of women with early-stage breast cancer. The exact role of these agents in adjuvant therapy of breast cancer, either sequentially with the "gold standard" tamoxifen or for the duration of therapy, has yet to be determined.

CONCLUSIONS

Recent studies with aromatase inhibitor agents are intriguing and suggest an improved side-effect profile and efficacy. The approval of these agents for the adjuvant treatment of breast cancer has led to a significant change in practice.

IMPLICATIONS FOR NURSING

Breast cancer is an extremely common cancer in women, and oncology nurses take care of large numbers of patients with this disease. Oncology nurses need the most recent information so they can discuss aromatase inhibitor agents and therapy with their patients.

Letrozole in the Extended Adjuvant Treatment of Postmenopausal Women with History of Early-Stage Breast Cancer Who Have Completed 5 Years of Adjuvant Tamoxifen

PURPOSE

To present the basis of the decision of the Food and Drug Administration to grant accelerated approval for letrozole for extended adjuvant treatment of early-stage breast cancer in postmenopausal women after completion of adjuvant tamoxifen.

EXPERIMENTAL DESIGN

The Food and Drug Administration reviewed the data from the MA17 trial, a single, multinational, randomized, double-blind, and placebo-controlled trial, submitted by the applicant to support the proposed new indication.

RESULTS

MA17 consisted of a core study and Lipid and Bone Mineral Density safety substudies. It enrolled 5,187 patients. In the core study, median treatment duration was 24 months and median follow-up duration was 27.4 months. Using a conventional definition of disease-free survival, 122 events on letrozole and 193 events on placebo were observed (hazard ratio, 0.62; 95% confidence interval, 0.49-0.78; P = 0.00003). Distant disease-free survival also improved with letrozole, 55 versus 92 events (hazard ratio, 0.61; 95% confidence interval, 0.44-0.84; P = 0.003). No statistically significant improvement in overall survival was observed. Hot flushes, arthralgia/arthritis, myalgia, and new diagnosis of osteoporosis were more common on letrozole. Frequency of fractures and cardiovascular ischemic events was not significantly different. A statistically significant mean decrease in bone mineral density in the hip occurred at 24 months on letrozole.

CONCLUSIONS

Letrozole administration led to a statistically significant prolongation in disease-free survival. Fractures and cardiovascular events were similar to placebo; however, new diagnoses of osteoporosis were more frequent. Short duration of treatment and follow-up precluded assessment of long-term safety and efficacy. Thus, accelerated approval was granted instead of regular approval.