Further stratification of data prompted (Figure 4): with OS as an endpoint, patients age >55 years (HR = 1.69, p = 0.010), non‐Hispanic (HR = 1.69, p = 0.011), T1 (HR = 1.88, p = 0.007), N0 (HR = 1.71, p = 0.008), no chemotherapy (HR = 1.54, p = 0.031), no systemic therapy (HR = 1.81, p = 0.037), non‐triple negative breast cancer (HR = 1.50, p = 0.039), ER positive (HR = 1.57, p = 0.028), PR positive (HR = 1.65, p = 0.026), histological grade II (HR = 1.99, p = 0.020) were more likely to benefit from IORT treatment. This evidence concerns the gene ESR1 and triple-negative breast carcinoma.