ATTOM trial

Background

6,953 women with early breast cancer (2,755 ER-positive; remainder ER-untested) on adjuvant tamoxifen were randomized to continue to 10 years or stop at 5 years, paralleling ATLAS.

Interventions and follow up

Arm A: Tamoxifen for 10 years
Arm B: Tamoxifen for 5 years (stop)
Primary endpoint: Recurrence and breast cancer mortality
mFollow up: NR

Results

Recurrence (10yr vs 5yr): RR 0.99 yr 5-6 (95% CI 0.86-1.15), 0.84 yr 7-9 (0.73-0.95), 0.75 later (0.66-0.86)
Breast cancer mortality: RR 1.03 yr 5-9 (0.84-1.27), 0.77 later (0.64-0.92)
Overall mortality: 849 vs 910 deaths, P=.1; RR 1.05 yr 5-9 (0.90-1.22), 0.86 later (0.75-0.97)
Endometrial cancer: 102 vs 45, RR 2.20 (1.31-2.34, P<.0001); 37 (1.1%) vs 20 (0.6%) deaths (absolute hazard 0.5%, P=.02)

Adverse events

Gynecologic: Endometrial cancer increased with 10 years (102 vs 45; RR 2.20, P<.0001), with excess endometrial cancer deaths (37 vs 20; absolute hazard 0.5%, P=.02).
Thromboembolic: Tamoxifen-class thromboembolic events as expected (specific rates NR in abstract).

Conclusions

10 years of tamoxifen reduces breast cancer recurrence from year 7 onward and mortality after year 10, consistent with ATLAS, at the cost of increased endometrial cancer.

Key Limitations

Reported as a 2013 ASCO abstract (not yet a full publication); many participants ER-untested, diluting benefit estimates. Late-emerging carryover benefit. No comparison with aromatase-inhibitor-based extended endocrine therapy.

Clinical Context

Pooled with ATLAS, provides the evidence base supporting 10 years of adjuvant tamoxifen for ER-positive early breast cancer (ASCO/ESMO endocrine-therapy guidance), informing extended-endocrine-therapy decisions in higher-risk patients.

References