Breast Cancer · Medical · Stage I–III · Extended adjuvant endocrine therapy

MA.17

After approximately five years of adjuvant tamoxifen, does five years of letrozole improve disease-free survival compared with placebo in postmenopausal women with hormone-receptor-positive breast cancer?

Trial registry: NCT00003140 · One underlying study; follow-up publications consolidated.

Design, population and eligibility

Design

Double-blind, placebo-controlled, phase III randomized trial; subsequently unblinded after early efficacy signal.

Population

5,187 postmenopausal women randomized after completing approximately five years of tamoxifen.

Eligibility

Postmenopausal, disease-free, hormone-receptor-positive early breast cancer after adjuvant tamoxifen; nodal status and prior chemotherapy stratified.

Maturity

Primary analysis at median follow-up 30 months; subsequent ITT analysis at median 64 months affected by crossover.

Treatment and comparator

Letrozole 2.5 mg orally once daily, planned for five years.

Matching placebo once daily; after unblinding, 66% of placebo-assigned patients accepted letrozole.

Primary endpoint: DFS, defined as recurrence or contralateral breast cancer.

Other endpoints: Distant DFS, OS, contralateral breast cancer, safety and quality of life.

Key efficacy results

At median follow-up 30 months, four-year DFS was 94.4% with letrozole versus 89.8% with placebo; HR 0.58 (95% CI 0.45–0.76), P<0.001.

Four-year distant DFS was 96.3% versus 94.9%; HR 0.60 (95% CI 0.43–0.84), P=0.002 in the initial update.

Four-year OS was 95.1% in both groups in the later ITT analysis; HR 0.82 (95% CI 0.57–1.19), P=0.30. A prespecified node-positive subgroup showed OS HR 0.61 (95% CI 0.38–0.98), P=0.04.

Source-reported outcome visualization

Four-year disease-free survival · 4 years

Letrozole

94.4%

Placebo

89.8%

Four-year Kaplan–Meier estimates from the updated primary report.

Absolute effect

Absolute four-year DFS improvement was 4.6 percentage points (94.4% versus 89.8%). Approximate NNT = 22 over four years, calculated from the fixed-time DFS estimates (1/0.046). This is not derived from median survival.

NNT: Approximately 22 to prevent one DFS event by four years; endpoint is DFS and horizon is four years.

NNH: Not calculated; no defensible fixed-horizon grade ≥3 harm rate in the cited primary analysis.

Toxicity, harms and treatment burden

Letrozole increased hormonally related adverse effects. In the initial report, fracture and cardiovascular-event incidence did not differ significantly from placebo; longer-term bone health remains clinically important.

After unblinding, crossover diluted randomized comparisons for later outcomes. Treatment duration and adherence should be considered in any interpretation.

Grade 3–5 toxicity and discontinuation due to adverse events are not reliably summarized in the abstract-level primary source; no numerical rates assigned.

Quality of life and patient-reported outcomes

MA.17 included overall and menopause-specific quality-of-life assessment. No large global QoL deterioration is inferred here; endocrine symptoms and musculoskeletal effects should be discussed individually.

Subgroups, maturity and limitations

The node-positive OS result is a subgroup finding and should not be promoted as a definitive overall-population survival benefit.

Premature unblinding and 66% placebo-to-letrozole crossover complicate long-term ITT interpretation.

MA.17 is distinct from MA.17R, which randomized patients after prior aromatase-inhibitor exposure; follow-up publications of MA.17 remain one underlying study.

Clinical interpretation

MA.17 demonstrated a clinically relevant reduction in recurrence after five years of tamoxifen with extended letrozole. The absolute four-year DFS gain was 4.6 points. The overall-population OS benefit was not established; node-positive subgroup findings require caution.

Current-practice context · 1 November 2026 (full guideline freshness review pending): Extended endocrine therapy is now risk-adapted and may involve aromatase inhibitor strategies after tamoxifen or initial AI therapy. Balance late recurrence risk against bone, musculoskeletal and cardiovascular health, prior endocrine exposure and patient preference.

Primary sources and registry

Source hierarchy: primary randomized report and prespecified follow-up first; registry and current guidance are supplementary. Values not reported in the cited primary sources are explicitly marked unavailable rather than imputed.

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