[en] Breast cancer is an aggressive disease whose incidence and mortality has increased in recent years. For this reason, it has aroused concern on the part of public health policies, being the target of research by the scientific community in the world. Among the treatments for breast cancer is radiotherapy, which uses ionizing radiation, however, with limitations due to its toxic effects on normal tissues. The development of drugs of plant origin associated with the treatment of radiotherapy is promising, since these substances modify the effects of radiation, minimizing its damage to the individual. The present study documents the trajectory of the studies that involved the adenocarcinoma cell lines (MDAMB-231) and human peripheral blood (PBMC) in the Ionizing Radiation Nucleus (NRI), in in vitro approaches and, therefore, the main objective was to evaluate in vitro effect of Aqueous Propolis Extract (EAP) on the cell viability of cells of the breast adenocarcinoma lineage and on the cell viability of human peripheral blood mononuclear cells The cell lines were irradiated with low LET (Linear Energy Transfer) radiation according to the kinetics of predetermined doses (2 and 5 Gy) and supplemented with EAP in concentrations of 1% and 10%. The post-irradiation collections were performed at the pre-established times of 24, 48 and 72 hours. The present study showed that the strains of MDAMB-231 and PBMCs showed different behaviors in vitro, and that ionizing radiation produced effects of significant decrease in the parameters of cell viability in PBMCs, while in the group of cells supplemented with EAP in addition to radiation, the damage caused has been minimized. With respect to MDAMB-231 breast adenocarcinoma cells, a reduction in the level of survival of these cells was observed when subjected to radiation, whereas this effect was enhanced when the cell culture was supplemented with aqueous extract of propolis. Supplementation with propolis extract in the treatment of radiotherapy offered quite measurable protection against damage to PBMCs cells. In addition, the propolis extract appears to potentiate cell apoptosis of radio-resistant breast adenocarcinoma cells. The data obtained through this investigation can serve as a subsidy for the use of propolis extract as an adjunct to the effects of radiotherapy treatment in patients with breast cancer. (author)