Radioresistance of tumors is not completely understood. Our previous studies have shown that MCF-7 breast cancer cell line exposed to 6 Gy and allowed to recover for 7 days (D7-6G) developed radio-resistance. In this study, we have tested the ability of these cells to form tumors in SCID mice and characterized these tumors by proteomic analyses. Untreated (MCF-C) and D7-6G cells (MCF-R) were injected s.c. in SCID mice and tumor growth monitored. On day 18, the mice were sacrificed and proteins were extracted from tumor tissues label free proteomic analyses was carried out by LC-MS.