Late risk of relapse and mortality among postmenopausal women with estrogen responsive early breast cancer after 5 years of tamoxifen

Background: Letrozole after 5 years of adjuvant tamoxifen results in a significant reduction in risk of recurrence from estrogen receptor (ER) positive breast cancer. An individualized estimate of the risk of relapse and death after 5 years of tamoxifen could improve decisions regarding extended hormonal therapy. Methods: The British Columbia Breast Cancer Outcomes database was used to identify women aged 45 years or older at the time of diagnosis with early-stage (I-IIIA) breast cancer who received tamoxifen and were disease free 5 years after diagnosis. Ten-year breast cancer event rates and mortality were calculated as well as annualized hazard rates of recurrence. Results: A total of 1086 women were identified with a median age of 64 years and follow-up of 10.5 years. The relative risk (RR) of death was 3.1 (P = 0.003) and for recurrence was 1.7 (P = 0.037) for N1 (one to three positive nodes) versus N0 (zero nodes positive) disease. N2 (four to nine nodes positive) had a RR of 5.8 (P < 0.001) for death and 3.0 (P = 0.002) for recurrence. Low tumor grade and high ER level subgroups had a more favorable prognosis. Annual breast cancer risk between years 6 and 10 was, respectively, 2.2%, 3.5% and 7.6% for N0, N1 and N2 disease and 2.6% and 4.5% for T1 and T2 breast cancer. Conclusion: T and N stages predicted late relapse and death from breast cancer in a population-based cohort of postmenopausal women. Risk estimates reported herein may be used to optimize decision making regarding adjuvant therapy after 5 years of tamoxifen.