Statistical analysis revealed no significant differences in age, surgical approach, molecular subtype, T/N stage, tumor location/quadrant, estrogen receptor/progesterone receptor status, human epidermal growth factor receptor 2 status, histological grade, the interval between radiotherapy and chemotherapy, and the method of dose escalation in the tumor bed among the patients (χ2 range: −0.917~4.511, t = 0.088, Z = −0.262, P > 0.05), as delineated in Table 2. This evidence concerns the gene ESR1 and neoplasm.