The morphological basis of human breast cyst populations.

Forty human cysts have been examined to determine the relationship between the epithelial lining and the content of sodium (Na+) and potassium (K+) in the cyst fluid. The ratios of Na+ to K+ for cysts lined by flattened epithelium were higher in all cases than the values obtained for cysts lined by apocrine epithelium. These findings suggest a morphological basis for the two populations of human breast cyst fluids which can be defined on cationic content.