Background
Phase III RCT (NCIC CTG MA.20). 1,832 women with node-positive or high-risk node-negative (N0 with T3, ER−, or grade 3 + T2 + LVI) breast cancer treated with BCS and adjuvant systemic therapy. Randomized to whole breast irradiation (WBI) alone vs WBI plus regional nodal irradiation (RNI) to the internal mammary nodes, supraclavicular and axillary apex (levels II–III). Enrolled 2000–2007.
Interventions and follow up
Arm A: WBI + regional nodal irradiation (RNI): internal mammary nodes + supraclavicular + axillary levels II–III (45 Gy/25 fx + breast boost)
Arm B: WBI alone (50 Gy/25 fx + optional boost)
Primary endpoint: Disease-free survival (DFS)
mFollow up: Median 9.5 year
Arm B: WBI alone (50 Gy/25 fx + optional boost)
Primary endpoint: Disease-free survival (DFS)
mFollow up: Median 9.5 year
Results
10-year DFS: 82.0% (RNI) vs 77.0% (WBI alone), HR 0.76 (95% CI 0.61–0.94), P=.01
10-year distant DFS: 86.3% vs 82.4%, HR 0.76 (95% CI 0.60–0.97), P=.02
10-year OS: 82.8% vs 81.8%, HR 0.91 (95% CI 0.72–1.13), P=.38 — not significant
10-year isoloated LRR: 2.9% vs 3.3% — not significantly different
10-year distant DFS: 86.3% vs 82.4%, HR 0.76 (95% CI 0.60–0.97), P=.02
10-year OS: 82.8% vs 81.8%, HR 0.91 (95% CI 0.72–1.13), P=.38 — not significant
10-year isoloated LRR: 2.9% vs 3.3% — not significantly different
Adverse events
Main adverse events: RNI vs WBI alone: Grade 2+ pneumonitis: 1.2% vs 0.2% (P=.01); Grade 2+ lymphedema: 8.4% vs 4.5% (P=.001). No significant difference in radiation pneumonitis requiring hospitalization or severe lymphedema. Cardiac toxicities were not significantly increased at 10 years.
Conclusions
Regional nodal irradiation (including IMN, SCV, and upper axillary nodes) added to whole breast RT improved 10-year DFS and distant DFS in women with node-positive or high-risk N0 breast cancer, at the cost of modestly increased pneumonitis and lymphedema. OS was not significantly improved at 10 years.
Key Limitations
Key Limitations: WBI alone arm did not include formal IMN/SCV RT — this may have underestimated the comparator if tangent fields are used without any RNI in practice. The OS benefit was not statistically significant despite meaningful DFS gains. Higher lymphedema rate (8.4%) with RNI is clinically significant. Trial was underpowered for OS. Most patients had 1-3 positive nodes — uncertain applicability to N0 high-risk patients where the benefit appears less certain. The specific contribution of IMN RT vs SCV/axillary RT is not separable within the RNI arm.
Clinical Context
MA-20 and EORTC 22922 together established RNI (including IMN) as a standard consideration for node-positive breast cancer patients. ASCO and ASTRO guidelines now recommend discussing RNI with patients with 1-3 positive nodes and strongly recommend it for ≥4 positive nodes. For SLNB-staged patients and for left-sided cancers, cardiac-sparing techniques (DIBH, prone positioning, IMRT) are used to minimize RNI-related cardiac dose.
References
References: Whelan TJ et al, N Engl J Med 2015 (MA-20)