Serum and intracystic levels of thyroxine (T4) and triiodothyronine (T3) in women with breast macrocysts.

In 15 patients with a total of 22 breast macrocysts serum and intracystic T4 and T3 and intracysts TSH were concomitantly radioimmunoassayed (using a technique with polyethylene glycol (PEG) for T3, T4, and a double antibody technique for TSH). While in most cysts (17/22) the T4 values were under those in the serum, in 21 cysts T3 was 2-18 times above the serum values. Intracystic TSH was at the lower limit of the normal serum TSH values whereas prolactin (PRL) and thyroglobulin (TGL) assayed in several cysts were not different from their serum value. It suggests that breast macrocysts are able to concentrate or even produce triiodothyronine.