PURPOSE: Breast cancer is the most common malignancy of women worldwide. Radiotherapy consists of a vital element in the treatment of breast cancer but relative side effects and different radioactive responses are limiting factors for a successful treatment. Doxorubicin has been used to treat cancers for over 30 years and is considered as the most effective drug in the treatment of breast cancer. There are also many chronic side effects that limit the amount of doxorubicin that can be administered. The combined radio-drug treatment, with low doses, can be an approach for reducing side effects from single modality treatments instead of suitable cure rates. METHODS: We have studied the effect of 1, 1.5, and 2 Gy doses of 9 MV X-rays along with 1 microM doxorubicin on inducing cell death, apoptosis and also p53 and PTEN gene expression in T47D and SKBR3 breast cancer cells. RESULTS: Doxorubicin treatment resulted in upregulation of radiation-induced levels of p53 and downregulation of PTEN at 1 and 1.5 Gy in T47D breast cancer cells, as well as downregulation of p53 mRNA level of expression and upregulation of PTEN mRNA level of expression in SKBR3 breast cancer cell line. In addition, doxorubicin in combination with radiation decreased the viability of breast cancer cell lines in the both cell lines. CONCLUSION: Low doses of doxorubicin, with least cell toxicity, may be an effective treatment for breast cancer when used in conjunction with ionizing radiation.