The pain in the rib cage under the right breast may be caused by the following conditions: 1) Inflammation of the rib cartilage or intercostal neuritis, which may be caused by viral infection or cold. 2) The pain may be caused by lesions in the chest, such as pleurisy and chest tumors. 3) The pain may be caused by lung disease. The pain may be caused by breast diseases, such as breast enlargement, mastitis and breast cancer, which may cause pain around the breast. 5. Considering that a variety of conditions can cause this symptom, it is best to go to the hospital for further diagnosis.