Galactoceles are cystic collections of retained milk, often caused by an obstructed milk duct. Galactoceles are benign, nonproliferative breast lesions.

Galactoceles tend to occur in females of reproductive age, typically around the time of delivery or during lactation. They are most common in patients who are pregnant or lactating due to their relationship to growth of mammary glands. The incidence of galactoceles in patients presenting with benign breast masses is estimated to be 4%, although true incidence is likely higher due to underreporting of asymptomatic or self-limiting masses.

Symptoms present gradually with a breast mass, which can become quite large. Risk factors for developing galactoceles include conditions that may lead to incomplete emptying of lactiferous ducts (eg, difficulty breastfeeding, breastfeeding is contraindicated), ductal obstruction (due to trauma, inflammation, prior breast surgery, or certain drugs that are galactagogues, such as domperidone and metoclopramide), or inappropriate prolactin secretion (eg, from medications, prolactinomas).

Rarely, galactoceles can present in nonlactating adults with galactorrhea secondary to excessive prolactin secretion from pituitary adenomas. Galactoceles are also a rare cause of breast enlargement in infants, likely due to transplacental prolactin stimulation.