Wenjie Ni, Xiunan Wang, Qin Wang, Yongqing Ge, Xiaofeng Mu

Department of Radiation Oncology, Beijing Shijitan Hospital, Capital Medical University, Beijing, People’s Republic of China

Correspondence: Xiaofeng Mu, Email muxiaof@sina.cn

Objective: To investigate the effects of radiation-induced lymphopenia (RIL) on survival in postmastectomy radiotherapy (RT) patients and identify relevant RIL predictive factors.
Methods: Patients with breast cancer who received postmastectomy radiotherapy at the study hospital were enrolled over June 2016 to December 2022. The peripheral blood counts were obtained before and during treatment and at the first posttreatment follow-up. Lymphopenia was graded according to the degree of lymphocyte reduction. The Kaplan–Meier method was used to compare disease-free survival (DFS) and overall survival (OS) between grade 0– 2 (G0-2) and grade 3 (G3) lymphopenia, and the Log rank test was used to compare between-group differences. DFS prognostic factors were determined through Cox regression analysis, and G3 lymphopenia predictive factors were assessed through logistic regression analysis.
Results: 156 patients with a median RT duration of 5.0 weeks were enrolled. During treatment, 29 (18.6%), 36 (23.1%), 67 (42.9%), and 24 (15.4%) patients had G0, G1, G2, and G3 lymphopenia, respectively. Over RT duration, the absolute lymphocyte counts continued to decrease until they reached the nadir at week 5. The median follow-up duration was 45.5 months. The 1, 3-, and 5-year DFS rates were 97.0%, 90.3%, and 87.4% in the G0-2 group, respectively; they were higher than those in the G3 group (83.3%, 69.2%, and 39.5%, respectively; p < 0.001). Cox univariate and multivariate analyses revealed that pathological stage and lymphopenia degree were independent prognostic factors for DFS (both p < 0.001). Logistic regression analysis revealed that low body mass index (BMI), integrated RT, and high heart (Dmean ≥ 6 Gy) and sternum (Dmean ≥ 20Gy) exposure dose were associated with G3 lymphopenia (all p < 0.05).
Conclusion: G3 RIL led to poor DFS in postmastectomy radiotherapy patients. BMI, RT modality, and heart and sternum exposure dose were noted to be independent RIL risk factors.

Keywords: breast neoplasm, postoperative radiotherapy, lymphopenia, prognosis