The causes of hard lumps in the breast are as follows: 1. If the lump is small and less mobile, the boundary is clear and not painful to the touch. If the lump is hard and painful to press, and if the lump is locally inactive, it is mostly caused by malignant hyperplasia of the breast, breast papilloma or early breast cancer. This is mainly because the cells inside the breast are affected by inflammation or other reasons, and the cells appear to be heterogeneous and proliferate, and the inflammation keeps invading the tissues and blood vessels around the breast, thus forming a hard lump. 3. mainly because women are in their normal physiological period, the breast will appear hard nodes in the breast under the regulation of hormones in the body.