Cystic breast masses and the ACRIN 6666 experience.

Masses due to cystic lesions of the breast are extremely common findings on mammography, ultrasonography, and magnetic resonance imaging. Although many of these lesions can be dismissed as benign simple cysts, requiring intervention only for symptomatic relief, complex cystic and solid masses require biopsy. Perhaps, the most challenging are complicated cysts, that is, cysts with internal debris. When the debris is mobile or a fluid-debris level is seen, complicated cysts can be dismissed as benign findings. As an isolated finding, homogeneous complicated cysts can be classified as probably benign, with intervention only considered with interval development or enlargement, abscess is suspected, or if suspicious features develop. When multiple and bilateral complicated and simple cysts are present (ie, at least three, with at least one in each breast), a benign, BI-RADS 2, assessment is usually appropriate. Clustered microcysts are common benign findings in pre- and perimenopausal women, though short-interval surveillance may be appropriate for many such lesions in post-menopausal women, particularly if the lesion is new or rather small or deep (ie, diagnostic uncertainty).