A complex breast cyst is a benign lesion that is one of the more serious types of breast cysts. Complex cysts are cystic nodules with both a cystic cavity and a solid nodule that form on top of cystic hyperplasia of the breast. Complex cysts are benign, but there is a certain risk of cancer, so once detected, radical mastectomy is often recommended, with close follow-up after surgery. There are also some complex breast cysts that can be followed up regularly after a puncture biopsy to clarify the nature of the cysts, without treatment for the time being. Some patients with complicated breast cysts are prone to localized infections, which may lead to acute mastitis or breast abscess, and require timely anti-inflammatory measures and drainage of abscesses.