Hard lump under the left chest may be caused by rib tumor, spleen rupture, pancreatic tail cyst and so on. 1. Rib tumor: including primary rib tumor and secondary rib tumor, hard lump can be touched under the left chest and accompanied by pain and pressure discomfort. 2. Splenic rupture: it refers to the rupture of splenic parenchyma due to the impact of some objects, which results in the symptoms of pain and mass, manifested as hard lump pain under the left chest. 3. Pancreatic tail cyst: It is a cystic mass in the tail of the pancreas caused by inflammation, trauma and tumor growth in the tail of the pancreas, which will cause pain and hard lump under the left chest. There are many causes of hard lump pain under the left chest, such as breast hyperplasia and breast malignant tumor in women. Patients should go to the hospital in time, clarify the cause of the disease under the guidance of the doctor and take effective treatment.