Swelling and pain in right breast after lung adenocarcinoma surgery may be caused by mastitis, lung cancer metastasis, pleural adhesion and so on. 1. Mastitis: Postoperative lung adenocarcinoma patients, especially those who need to undergo chemotherapy, are vulnerable to invasion of various pathogens with weak immune function, and when the right breast is infected by bacteria, mastitis may appear, which may be manifested as redness, swelling, heat and pain in the breast. 2. Lung cancer metastasis: lung adenocarcinoma belongs to malignant tumors, if it continues to develop, it can metastasize to the surrounding tissues, and when it metastasizes to the right breast, it can cause pain in the right breast. 3. Pleural adhesion: after lung adenocarcinoma surgery, patients may have pleural cavity adhesion, which may pull the pleura when taking deep breaths and lead to chest pain, and the location is mostly concentrated in the chest and breast area; right breast pain may occur after right lung adenocarcinoma surgery. It is recommended to go to the hospital and ask the doctor to make judgment and treatment when there is swelling and pain in the right breast after lung adenocarcinoma surgery.