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 (T 4 ), free T 4 and free triiodothyronine (T 3 ) 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 T 3 levels were higher in BCF than in serum (p < 0.001), whereas T 4 , free T 4 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 T 3 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 T 3 concentration. Free T 3 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 T 3 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 T 4 or T 4 in BCF. These data suggest an important role of free T 3 in the physiology of fibrocystic breast disease.