Background: Surgery and radiotherapy are two main modalities of breast cancer treatment. However, surgery affects the tumor microenvironment negatively and promotes the growth of possible malignant cells remaining in the tumor bed. Objective: The present study aimed to investigate the effects of intraoperative radiotherapy (IORT) on the tumor microenvironment. Therefore, the effect of surgical wound fluid (WF), collected from operated and irradiated patients on the growth and motility of a breast cancer cell line (MCF-7) was assessed. Material and Methods: In this experimental study, preoperative blood serum (PS) and secreted WF from 18 patients who underwent breast-conserving surgery (IORT-) and 19 patients who received IORT following surgery (IORT+) were collected. The samples were purified and added to MCF-7 cultures. Two groups of the cells were treated with and without fetal bovine serum (FBS) and used as positive and negative controls. Applying 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and scratch wound healing assays, the growth and motility of MCF-7 cells were measured. Results: Cell growth of the cells receiving WF from IORT+ patients (WF+) was statistically higher than the corresponding values of the cells received PS or WF from IORT- patients (WF-) (P < 0.01). Both WF+ and WF- decreased the cells’ migration ability compared to PS (P < 0.02) and FBS (P < 0.002), although WF+ caused a more significant reduction (P < 0.02). Conclusion: Wound fluid extracted from breast cancer patients who underwent both surgery and IORT increased the growth of breast tumor cells, but decreased their ability to migrate.

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