The Absolute Effect / Breast Cancer / Radiation
After lumpectomy for node-negative invasive breast cancer ≤1 cm, can tamoxifen substitute for breast irradiation, and does adding tamoxifen to irradiation improve local control?
1,009 women with node-negative invasive breast cancer ≤1 cm treated with lumpectomy and axillary dissection; randomized to tamoxifen alone (n=336), breast RT + placebo (n=336), or breast RT + tamoxifen (n=337).
Tamoxifen for 5 years versus breast irradiation versus breast irradiation plus tamoxifen. This was a 3-arm randomized comparison.
At 8 years, ipsilateral breast tumour recurrence was 16.5% with tamoxifen, 9.3% with RT alone and 2.8% with RT + tamoxifen. Thus RT + tamoxifen reduced IBTR by 13.7 percentage points versus tamoxifen alone (NNT ≈ 8 over 8 years) and by 6.5 points versus RT alone (NNT ≈ 16). RT alone reduced IBTR by 7.2 points versus tamoxifen (NNT ≈ 14).
Distant treatment failure and overall survival did not significantly differ among groups; 8-year survival was approximately 93–94% across arms.
The trial predates contemporary hypofractionation and modern systemic therapy. The major clinically relevant burden is the additional treatment associated with breast irradiation and/or endocrine therapy; comparative grade 3–5 toxicity reporting is limited by the era.
In small node-negative invasive breast cancer, tamoxifen did not provide local control equivalent to breast RT. Combining RT and tamoxifen produced the lowest ipsilateral recurrence, while the trial did not demonstrate a survival difference.
NSABP B-21 results summarized with trial design and 8-year outcomes.
NSABP B-21 showed that radiotherapy after lumpectomy substantially reduces ipsilateral recurrence in small node-negative breast cancer, with tamoxifen contributing systemic and local benefit. Contemporary omission of RT is limited to selected low-risk patients under modern criteria; assess age, biology, margins, endocrine adherence, life expectancy and patient preferences.