Review of complex breast cysts: implications for cancer detection and clinical practice.

The use of ultrasound in breast diagnosis has resulted in the increasing identification of incidental benign-appearing lesions, of which complex (or atypical) breast cysts are frequently reported. Complex breast cysts were estimated to be reported in approximately 5% of breast ultrasound examinations. A systematic review of the literature on sonographically detected complex breast cysts was carried out. The quality of primary studies and extracted data on cancer detection was assessed. Very few studies have examined complex breast cysts and quantified the associated cancer detection rate. In most of these studies, subjects have been selected on the basis of progress to intervention, which would overestimate the likelihood of malignancy. The only study to examine complex cysts from all consecutive ultrasounds reported one case of non-invasive cancer from 308 lesions--0.3% (95% confidence interval, 0.01-1.84). Ultrasound features associated with a higher risk of the lesion being a cancer are: thickened walls, thick internal septations, a mix of cystic and solid components, and an imaging classification of indeterminate. Using the information from the present review, complex breast cysts were categorized on the basis of associated risk of malignancy, and an approach to the management of these lesions to assist clinical decision-making was suggested. Provided adequate information is given to the patient, complex breast cysts with a very low risk of malignancy do not always require image-guided biopsy.