Breast cyst type does not predict the natural history of cyst disease or breast cancer risk.

The sodium (Na) and potassium (K) concentrations were measured in the fluid of 169 breast cysts aspirated from 101 consecutive patients presenting to a single clinic. The Na/K ratio was used to define cysts as either apocrine (Na/K less than 3) or flattened (Na/K less than 3) in type. There was no consistency in the type of cyst for individual patients. Cyst type was not predictive of further cyst development, neither was a particular cyst type associated with the development of, or a history of, breast cancer.