Abstract P5-10-17: Radiotherapy-induced miR expression influences the formation of local recurrence in breast cancer

Abstract

Abstract In early breast cancer (EBC) patients, local disease relapse occurs at the site of the original primary tumor in 90% of cases and the addition of external beam radiotherapy (EBRT) after surgery is necessary to reduce recurrence rate. This observation suggested that surgery itself could represent a perturbing factor, possibly by altering the local microenvironment by inducing a wound healing response. Recent evidences indicate that, in selected EBC patients, 5 weeks of EBRT can be successfully replaced by a single dose of Targeted Intraoperative Radiotherapy (TARGIT). Interestingly, TARGIT acts not only affecting tumor cell survival itself, but is also able to alter the tumor microenvironment, by modifying cytokines secretion and activation of several intracellular pathways in breast cancer cells. In order to understand the significance of these modifications in breast tumor microenvironment after exposure to TARGIT we set up a mouse model of TARGIT treatment. Our results highlighted that the act of surgery alone strongly stimulates breast cancer cell growth and the addition of local irradiation completely reverses the surgery-induced breast cancer cell growth. Moreover, we evaluated the impact of TARGIT by analyzing microRNA (miR) expression both in our mouse model and in human specimens. To this aim, we collected paired specimens of peri-tumoral mammary tissues from 30 early breast cancer (EBC) patients, before and after treatment with TARGIT. Microarray approach followed by qRT-PCR validation revealed the presence of specific TARGIT-regulated miRs. Among the others, miR-223 was the most highly and significantly modified. In silico analyses indicated that epidermal growth factor (EGF) is a potential candidate of mR-223 regulation. In vitro experiments, using both normal and tumor derived cell lines validated the bioinformatic prediction, demonstrating that the 3′ UTR of EGF is a target of miR-223 and this binding results in the control of EGF production by the cells. Importantly, miR-223 overexpression was able to impair, at least in part, the wound-induced growth of normal and tumor derived breast-cancer cells, eventually influencing breast cancer cell proliferation and survival. Our results suggest that the effects of radiotherapy in the wounded tissue go far beyond the mere killing of residual tumor cells and is able to balance the negative effects of the wound healing process, both in human and mouse breast tissue. TARGIT-induced microenvironment modifications, in particular miR-223 up-regulation, significantly impair breast cancer response to surgery-induced inflammation eventually resulting in recurrence control. Our experimental findings strongly support the notion that the timely application of radiotherapy to the tumor bed, immediately after tumor removal, is critical to counteract the effects of surgery and wound healing process on residual breast cancer cells and normal peri-tumoral breast tissue. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-10-17.