Thyroid hormones in fibrocystic breast disease.

This study was undertaken to evaluate the role of thyroid hormones in fibrocystic breast disease. The concentrations of thyroid-stimulating hormone (TSH), thyroxine (T4), free T4 and free triiodothyronine (T3) were determined in serum of 50 women with fibrocystic breast disease without macrocysts (cysts of over 3 mm diameter) and in the serum and breast cyst fluid (BCF) of 60 women with fibrocystic breast disease and macrocysts. Possible relationships between thyroid hormones and estradiol, dehydroepiandrosterone sulfate, testosterone, progesterone and 17-hydroxyprogesterone in the BCF also were analyzed. Serum thyroid hormone levels did not differ between the two groups. Free T3 levels were higher in BCF than in serum (p < 0.001), whereas T4, free T4 and TSH concentrations were lower in BCF as compared to serum (p < 0.001). Cysts were divided according to their K+/Na+ ratio because a ratio above 3 represents a predictor of malignant transformation. Free T3 concentrations were higher in BCF than in serum, in both low K+/Na+ cysts and in cysts with a K+/Na+ ratio above 3; those cysts with a high K+/Na+ ratio had the highest free T3 concentration. Free T3 in cysts correlated positively to the K+/Na+ ratio (r = 0.831; p < 0.001). Multiple linear regression analysis demonstrated that the concentration of free T3 in BCF was predicted statistically by the positive regression coefficient for the estradiol concentration. No candidate variable was included in the model to predict concentrations of TSH, free T4 or T4 in BCF. These data suggest an important role of free T3 in the physiology of fibrocystic breast disease.