A study published in JAMA Oncology found that tamoxifen produced a long-term protective affect for women with luminal A and luminal B breast cancer subtypes.
Researchers used data from a secondary analysis of the Stockholm Tamoxifen trial that was conducted from 1976 to 1990, which randomized postmenopausal patients with lymph node-negative breast cancer to receive at least two years of adjuvant tamoxifen or no endocrine therapy.
The current study only included patients with luminal A or B subtype tumors. Complete long-term follow-up data through December 31, 2012, were obtained from the Swedish National registers. Patients without recurrence who reconsented were further randomized to an additional three years of tamoxifen therapy or no endocrine therapy.
In the original treated trial arm, 183 patients had luminal A tumors and 64 patients had luminal B tumors. In the untreated arm, 153 patients had luminal A tumors and 62 had luminal B tumors. Patient age at diagnosis ranged from 45 to 73 years.
Improved recurrence-free interval with tamoxifen
Researchers observed a statistically significant difference in distant recurrence-free interval (DRFI) by trial arm (P<0.001). Among treated patients, the 25-year DRFI for luminal A was 87% (95% CI, 82-93) and 67% (95% CI, 56-82) for luminal B. Among untreated patients, the 25-year DRFI was 70% (95% CI, 62-79) and 54% (95% CI, 42-70), respectively.
Patients with luminal A tumors significantly benefited from tamoxifen therapy for 15 years after diagnosis (hazard ratio [HR] = 0.57; 95% CI, 0.35-0.94), while those with luminal B tumors benefited from tamoxifen therapy for five years (HR=0.38; 95% CI, 0.24-0.59).