Comparative analysis of the effect of different radiotherapy regimes on lymphocyte and its subpopulations in breast cancer patients

The aim of this study was to determine whether different radiotherapy (RT) fractionation schemes induce disparate effects on lymphocyte and its subsets in breast cancer patients. 60 female patients diagnosed with breast cancer were recruited in this study after receiving modified radical mastectomy and were randomly divided into two groups. One group received irradiation at a standard dose of 50 Gy in 25 fractions and the other at a dose of 40.3 Gy in 13 fractions. Both total lymphocyte count and its composition were recorded at three timepoints: right before the radiation treatment (T0), immediately after the last fraction of radiotherapy (T1) and 6 months after irradiation therapy ended (T2). Both groups experienced temporal lymphopenia after finishing local radiation (T1) (13F T0 vs. T1 1570.6 +/- 243.9 vs. 940.6 +/- 141.8, **p < 0.01; 25F T0 vs. T1 1620.5 +/- 280.2 vs. 948.5 +/- 274.6, **p < 0.01), while the lymphocyte count recovered at follow-up time (T2), and the cell count in the hypofractionation group (13F) was higher than the standard fraction group (25F) (13F vs. 25F 1725.6 +/- 225.6 vs. 1657.5 +/- 242.4, *p < 0.05). With respect to the composition of lymphocyte, we found T cell, B cell, and NK cell reacted differently to different radiotherapy protocols. Different RT protocols impose different impacts on immunity, leading us to further explore the optimal radiotherapy regimes to synergy with immunotherapy.