The bone pain under the left armpit of men in their fifties may be related to lymphatic enlargement, intercostal neuritis, tumor and other reasons. 1. Lymphatic enlargement: when the left side of the patient’s chest has trauma, inflammation, infection, etc., it causes localized inflammation, exudation, or even necrosis of lymph nodes, so it leads to left armpit pain. 2. Intercostal neuritis: due to viral infection or osteophyte, etc., the intercostal nerves in the left armpit are damaged for different reasons and inflammatory reaction occurs, which then causes pain in the left armpit. 3. Tumor: when the chest wall or breast tumor metastasizes to the left axillary lymph node, when the tumor invades the lymphatic tissues, it will also cause the left axillary nerve and muscle pain, and then it is necessary to do the lymph node biopsy for clear diagnosis. When men in their fifties have bone pain in the left armpit, it is recommended to consult a doctor in time, follow the doctor’s instructions for further examination, and carry out targeted treatment or therapy with the help of the doctor.