Left sternal pain may be caused by trauma, costochondritis, bone tumor, leukemia and so on. 1. Trauma: trauma leads to local soft tissue injury or sternal fracture, manifested as chest pain, chest tightness, and pain aggravated by coughing and deep breathing. Localized skin lesions or bruises can be seen. 2. Costochondritis: manifested as pain in the front chest wall, swelling and bulging of the affected costochondral area gradually, pain is obvious when pressing, and the pain can be radiated to the axilla, shoulder and other parts. 3. Bone tumor: occurring in the bone or originating from the bone tissue components of the tumor, usually pain, local mass, dysfunction, pathological fracture as a typical manifestation, with the progress of the disease may appear pressure pain. 4. Leukemia: malignant neoplastic disease of hematopoietic system, bone pain is one of the common signs, the location is not fixed, mainly in the sternum, limb bones, etc., often the pain is more intense, the effect of painkillers is not good. Left chest bone pain can also be seen in other causes, it is recommended that patients seek medical treatment as soon as possible to avoid delaying the condition.