Background: Few studies have evaluated the effects of adjuvant radiotherapy (RT)of breast cancer(BC). The relation between the risk of lung carcinoma and radiotherapy have been controversial. Methods and materials: We retrospectively studied 127 patients treated at the Institut Curie with non metastatic breast cancer and lung carcinoma between 2000 and 2011(2/3 of BC apperead befor lung). Confirmation Diagnosis bronchial cancer obtained by: biopsy: histological data:architecture, IHC (HR, HER 2, TTF1), EGFR, Kras statut clinical and radiological Correlation. Comparison with breast tumor Results: BC: median age at diagnosis 54 years, predominatly invasive ductual carcinoma(IDC), lumpectomy 78%, mastectomy 21%. Lung cancer: median age at diagnosis: 63 years, 67 smokers. histology: 52 % Adenocarcinoma, 18.1 % scamous cell carcinoma, 18.1% large cell carcinoma, 13.4 % small cell carcinoma. EGFR mutation in 4.3%. 109 patients underwent RT (3 cases of lung cancer befor BC):Region: internal mammary chain: 46, supracalvicular: 42, axillary: 21. Technique: lateral decubitus position: 44, dorsal decubitus position: 57. Interval between breast and lung cancer: 0–3 years: 24.4%, 3–5 years: 15%, 6–10years: 16.5%, 11–20 years: 28%, >20 years: peak of incidence of lung cancer in the 3 years of diagnosis of breast cancer: 24.4 %. There was no apparent relation between treatment of BC and relative risk of developing lung carcinoma. 2nd peak between 11–20 years: 32 % patients, suggest that RT may increase risk of lung carcinoma (latency period for radiation induced second malignancy). Conclusion: This study suggest that adjuvant RT is associated with a real but small risk of developing lung carcinoma. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-13-14.