Experimental Factor Ontology identifier EFO_1000848 (breast cyst) can be described as follows. A fluid-filled closed cavity or sac that is lined by an EPITHELIUM and found in the BREAST. It may appear as a single large cyst in one breast, multifocal, or bilateral in FIBROCYSTIC BREAST DISEASE. Also known as: Breast Cyst, Cyst of breast, Cyst of breast (disorder), Cyst of the breast.