When the C8A biomarker entered the model as a continuous variable, a statistically significant treatment-by-biomarker interaction was detected only in the multivariable model (P = .0062 adjusted for estrogen receptor local, tumor grade, nodal status, and region; Data Supplement), whereas no significant predictive effect was observed in the simple model (P = .07). The gene discussed is ESR1; the disease is neoplasm.