Are there diseases that cause non-cancerous breast lumps?

Yes: The breast, by it's very nature, is "lumpy-bumpy", so most lumps are actually just normal breast tissue. When a distinct lump is found (a "dominant mass"), it may be a fluid-filled lump called a cyst, which is very commen and totally benign. Of course, a new lump may be a tumor, however many of these are benign, as well. In order to sort through this maze, it is always best to see your doctor.

Yes: The commonest reason for benign breast lumps is fibrocystic change which is caused by the menstrual cycle hormonal effect on the breast tissue. Benign fibroadenomas are common causes of breast masses.

Cyst?: Could be cyst, a site of infection, a benign tumor such as a fibroadenoma.