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Top Line: Breast cancer genomic risk is coming to a regional nodal irradiation treatment algorithm near you.
The Study: SweBCG 91 RT was a trial of nearly 1200 women with early stage (I-II), node-negative breast cancer who underwent a margin-negative lumpectomy. They were randomized to adjuvant whole breast radiation (without a boost) versus observation. At the time, only a fraction of patients received adjuvant chemo or endocrine therapy—so this study gives a fairly pure look at radiation effects. The Adjuvant Radiation Intensification Classifier (ARTIC) is a genomic classifier validated on nearly 1000 tumor samples in this cohort. The model uses 27 genes plus patient age to calculate the risk of locoregional recurrence (LRR). A “high” score was defined as the 75th percentile or higher and was associated with an increased risk of LRR regardless of radiation. ARTIC was also predictive of benefit with radiation-—but not like you’d think. Remembering that no nodal radiation was used in the validation trial, it was actually patients with low scores who derived a greater LRR benefit from radiation. That’s because patients with high scores were much more likely to have a regional recurrence (11% versus <1%) even with radiation. So, ARTIC doesn’t tell us who can omit radiation...because everyone benefits. What it tells us is who has less benefit from breast-only radiation.
TBL: ARTIC is a 27 gene + age classifier that is both prognostic of locoregional recurrence and predictive of breast-only radiation benefit in women with early stage, node-negative breast cancer. | Sjostrom, J Clin Oncol 2019