A small round lump in the breast may be a normal breast structure, or it can be caused by breast nodules, breast fibroadenoma, breast cysts, and other reasons. 1. Breast nodule: Breast hyperplasia caused by hormone levels and emotional factors can lead to breast nodules being detected in the breasts, which can also be accompanied by breast swelling and pain. 2. Breast fibroadenoma: Breast fibroadenoma is more common in young women. Some of them can be touched on the surface of the body as a tough, rounded lump, usually with good mobility. 3. Breast cysts: Breast cysts are mostly due to the stagnation of milk, resulting in cystic dilatation of the milk ducts. Most of them are round or oval with clear boundary and smooth surface. If you find a round lump in your breast, you should also consider mastitis, breast trauma, malignant tumors, etc. You should consult a doctor as soon as possible to make a clear diagnosis.