Nomogram predicting survival as a selection criterion for postmastectomy radiotherapy in patients with T1 to T2 breast cancer with 1 to 3 positive lymph nodes

Background The role of postmastectomy radiotherapy (PMRT) in women with pT1‐T2N1 breast cancer is controversial. The authors developed a nomogram that was predictive for overall survival (OS) and identified patients who derived no benefit from PMRT. Methods The authors retrospectively evaluated 4869 patients with pT1‐T2N1 breast cancer who were treated with mastectomy between 2000 and 2014 in 11 Chinese hospitals. Rates of locoregional recurrence and distant metastasis were calculated using competing risk analysis, and disease‐free survival and OS rates were calculated using the Kaplan‐Meier method. Based on the risk factors identified from Cox regression analysis in 3298 unirradiated patients, a nomogram predicting OS was developed. The benefit of PMRT was evaluated in different risk groups stratified by the nomogram model. Results After a median follow‐up of 65.9 months, the 5‐year OS, disease‐free survival, locoregional recurrence, and distant metastasis rates were 93.3%, 84.3%, 5.2%, and 8.3%, respectively. A total of 1571 patients (32.3%) underwent PMRT. On multivariable analyses, PMRT was found to increase OS significantly (hazard ratio, 0.61; P = .002). An OS prediction nomogram evaluated the effect of age; tumor location; tumor size; positive lymph node ratio; estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 status; and treatment with trastuzumab. Based on nomogram scores, the entire patient cohort was classified into 3 risk groups. PMRT significantly improved the OS of patients in the intermediate‐risk ( P < .001) and high‐risk groups ( P = .004), but not in the low‐risk group ( P = .728). Conclusions The authors developed a nomogram that is predictive of OS among women with pT1‐T2N1 breast cancer after mastectomy. This nomogram may help to select a subgroup of patients with a good prognosis who will not benefit from PMRT.