Background
ABCSG-16 / Secondary Adjuvant Long-term Study with Arimidex (SALSA). Phase III RCT of 3,484 postmenopausal women with HR+ breast cancer who were disease-free after 5 years of adjuvant endocrine therapy (72.3% T<2cm, 66.3% node-negative). Compared 2 vs 5 additional years of anastrozole.
Interventions and follow up
Arm A: Anastrozole 1mg/d po for 2 additional years after 5yr of endocrine therapy
Arm B: Anastrozole 1mg/d po for 5 additional years after 5yr of endocrine therapy
Primary endpoint: DFS
mFollow up: 118mo (~9.8yr)
Arm B: Anastrozole 1mg/d po for 5 additional years after 5yr of endocrine therapy
Primary endpoint: DFS
mFollow up: 118mo (~9.8yr)
Results
8-yr DFS: 73.6% (2yr) vs 73.9% (5yr); HR 0.99, 95%CI 0.85–1.15; P=.90
OS: No significant difference between arms
OS: No significant difference between arms
Adverse events
Musculoskeletal: Bone fractures higher with 5 additional years 6.3% vs 4.7% (HR 1.35, 95%CI 1.00–1.84)
Overall: No excess of other serious adverse events with the longer (10-year) duration
Overall: No excess of other serious adverse events with the longer (10-year) duration
Conclusions
No DFS or OS difference between 2 vs 5 additional years of anastrozole (i.e., 7 vs 10 total years of endocrine therapy); the longer duration increased fracture risk. Two additional years is sufficient for most patients.
Key Limitations
Lower-risk, predominantly node-negative population (66% N0), limiting power to detect benefit of prolonged therapy in higher-risk patients. Both arms received extension, so the trial informs optimal duration rather than whether to extend. No genomic risk stratification.
Clinical Context
Key duration trial showing diminishing returns and added bone toxicity beyond ~7 total years of endocrine therapy. ASCO/ESMO recommend individualizing extended endocrine therapy by recurrence risk; SALSA supports limiting extension to ~2 additional years for many patients.