NSABP B-20
In node-negative, ER-positive breast cancer, does adding adjuvant chemotherapy to tamoxifen improve recurrence and survival?
Absolute Effect
Long-term follow-up showed substantially fewer recurrences with chemotherapy plus tamoxifen than tamoxifen alone.
The survival advantage was directionally favourable but did not reach conventional statistical significance in the long-term report (P=.063).
The original trial is best understood as evidence that chemotherapy can add benefit to endocrine therapy in selected node-negative ER-positive disease; the absolute benefit varies markedly with baseline genomic risk.
Clinical interpretation
In the prospective-retrospective 21-gene analysis, patients with high recurrence scores derived a large chemotherapy benefit, whereas patients with low scores derived minimal or no apparent benefit.
Limitations
The chemotherapy regimens and endocrine therapy used in B-20 predate contemporary taxanes, HER2-directed therapy, aromatase inhibitors and genomic-risk-guided treatment. Therefore the trial's relative evidence is foundational, but its raw event rates are not contemporary baseline risks.
NNT / NNH
A single overall NNT is not displayed because the clinically meaningful benefit is strongly modified by recurrence risk. The later 21-gene analysis reported a 27.6-percentage-point absolute reduction in 10-year distant recurrence for high-risk (RS ≥31) tumours, corresponding to an approximate NNT of 4 in that analysed subgroup.
NNH is not calculated from the pivotal efficacy report because a single fixed-time serious-toxicity endpoint is not appropriate for the historical regimen.
Primary / authoritative sources
NSABP B-20 primary report — PubMed