Cyst in ovary: An ovarian cyst is a sac

An ovarian cyst is a sac filled with fluid or a semisolid material that forms on or inside the ovaries . Usually harmless, sometimes they require removal. Ovarian cysts are fluid-filled pockets that grow on the ovaries . Almost all ovarian cysts are non-cancerous (benign), but some are cancerous (malignant), or may become cancerous over time. Many people with ovarian cysts don't have any symptoms or require any treatment, as many go away on their own. An ovarian cyst forms when fluid collects in a membrane of an ovary . Large cysts can cause symptoms, such as pain. In rare cases, a cyst can become cancerous. Learn more. Learn about ovarian cysts, fluid-filled sacs that form on or inside your ovaries. Find out the common types, how they affect your health and how to diagnose and treat them.