A cumulus cyst is actually a blister-like structure with a very thin skin and then fluid wrapped inside, so whenever a nodule or swelling is said to be a cyst, it must be a mass of fluid wrapped in a thin skin. Most of the reasons for breast cysts are related to the accumulation of a large amount of milk in the lobules of the gland during lactation without timely emptying. Due to the high pressure of the milk, some of the lobules are swollen, which means that they become a cavity and the structure is destroyed. The milk can no longer be drained from the distended cavity, so it will wrap up and form a cumulus cyst, which actually does not have any potential risk of malignancy or affecting a person’s health, and does not require any treatment.