Pain in the rib cage below the armpit generally has several causes: first, tumors in the rib cage itself. Osteoma, bone-like osteoma or other benign tumors can occur in the rib cage. X-rays should be performed to further confirm the diagnosis. Secondly, metastatic tumors of the rib cage. Especially in the armpit, it is important to touch the armpit to see if there are enlarged lymph nodes. In breast cancer, lymph node metastasis in the armpit often occurs, and it can be accompanied by metastasis in the rib cage. In this case, a whole-body bone scan or CT scan and examinations of other areas such as lung, prostate, liver or thyroid should be performed to rule out the presence of the primary tumor. Third, intercostal neuralgia. There is intercostal nerve distribution around the rib cage. When the intercostal nerve is involved for various reasons, intercostal nerve pain will occur, which can then manifest as pain in the rib cage.