Cytological and biochemical studies of breast cyst fluid.

We determined the biochemical composition of fluid aspirated from 52 breast cysts and classified the cysts into types I and II on the basis of the potassium-to-sodium (K/Na) ratio in the fluid. In this study, we confirmed the presence of prostate-specific antigen (PSA) in some breast cyst fluids, regardless of whether cysts were type 1 or type 2, or benign or malignant. On immunohistochemical study, we found no direct correlation between the presence of PSA and progesterone receptors, which is at odds with the results of earlier reports. Current practice in cytologic study appears to favor the examination of bloody fluid. In this study, two samples found to contain malignant cells were cloudy or turbid. We therefore recommend that all cloudy or turbid cyst fluids should be subjected to cytologic examination. This study indicated that the potassium and sodium concentrations were not the same in multiple cysts in the same individuals. In addition, apocrine cells were observed in both type 1 and type 2 cysts. Therefore, breast cyst type cannot predict the natural history of cystic changes or indicate the likelihood of cancer. The finding of malignancy in two patients with type 2 cysts also supports this argument.