Benign changes characterized by the formation of fibrotic and/or cystic tissue.- Most common benign lesion of the breast- Up to 50% of women are affected during their lifetime

Etiology: unknown

Clinical features:- Premenstrual bilateral breast pain- Tender or nontender breast nodules- Clear or slightly milky nipple discharge

Diagnosis:- Physical exam- First-line: ultrasound and mammogram- Fine-needle aspiration- Biopsy:→ Stromal fibrosis→ Cysts→ Papillary apocrine changes→ Mild epithelial hyperplasia → Calcifications

Treatment:- If mild: none- If severe symptoms: oral contraceptives, tamoxifen or progesterone