In premenopausal women with estrogen receptor–positive primary breast cancer, 2 years of adjuvant tamoxifen resulted in the long-term reduction of breast cancer–related mortality, compared with patients who received no systemic treatment, a phase III randomized trial showed.
Tamoxifen is the endocrine therapy of choice for most premenopausal patients with ER-positive disease, wrote Dr. Maria Ekholm and her colleagues. “The long-term effect reported in this study is particularly important for young patients with a potentially long life expectancy who are at risk for late relapse, as is commonly seen in [estrogen receptor]-positive breast cancer.”
In the phase III trial, the investigators randomized 564 (362 ER-positive) premenopausal women with stage II breast cancer: 276 received tamoxifen and 288 received no adjuvant treatment, reported Dr. Ekholm, an oncologist at Lund (Sweden) University and her colleagues (J Clin Oncol. 2016 May 9. doi: 10.1200/JCO.2015.65.6272).
Among the group with ER-positive tumors, patients younger than 40 years had the greatest mortality reduction (less than 40 years: hazard ratio, 0.37; 95% confidence interval, 0.17-0.82; greater than 40 years: HR, 0.87; 95% CI, 0.61-1.22; interaction P = .044). Of the 314 deaths, 262 were breast cancer related. Also, tamoxifen had a greater effect in the patient subgroup with grade 3 tumors, compared with subgroups with grade 1 or 2 tumors, Dr. Ekholm and her colleagues found.
ER-positive patients had a high fatality rate during the first few years of follow-up, and tamoxifen had no effect during this time. Tamoxifen’s beneficial effect on cumulative mortality and cumulative breast cancer–related mortality was highest during years 5-15 of follow-up, with relative mortality reductions of nearly 50%, compared with the control group.
“The positive effect of tamoxifen was weaker for the last follow-up period (greater than 15 years), including fewer events and hence lower power, but the [hazard ratios] and estimates of [cumulative mortality] and [cumulative breast cancer–related mortality] indicate a possible carryover effect beyond 15 years,” the investigators wrote.
Dr. Ekholm reported financial ties to Amgen. Two coauthors also reported ties to industry sources.