A large bag on the left rib cage is mainly considered to be caused by abnormalities of the rib cage and the surrounding tissues, and the causes of the corresponding conditions include osteochondroma, fracture scab formation, malignant tumors, and peripheral soft tissue lesions. 1. Osteochondroma: Osteochondroma around the ribs will cause bony protrusions, leading to the corresponding conditions. 2. Fracture scab formation: after a rib fracture, a scab will form around the rib during the healing process, which will also cause corresponding changes. 3. Malignant tumor: lung cancer can cause invasion and damage to the neighboring ribs, resulting in soft tissue mass, or other parts of the tumor metastasize to the ribs, which will cause corresponding changes. 4. Peripheral skin and soft tissue lesions: mainly including lipoma and sebaceous adenoma, etc., which may cause corresponding changes and are related to the abnormal proliferation of local tissue cells. There may be other reasons for the growth of a large bag on the left rib cage, so please consult a doctor in time to diagnose the specific cause through clinical examination and carry out standardized treatment under the guidance of clinicians to avoid delaying the condition.