There has been much controversy concerning the detection of plasma TGF-beta (1) levels in breast cancer patients. The present study provides preliminary evidence on underestimated plasma TGF-beta (1) levels due to ex vivo proteolysis and previous therapeutic treatment of breast cancer patients, as detected by a commercial ELISA immunoassay. Our results revealed that the addition of protease inhibitors: phenylmethylsulfonyl fluoride and aprotinin, to the plasma preparation of healthy volunteers, has increased TGF-beta (1) median Value from 3.1 ng/mL to 33.9 ng/mL. Relative to that, in protease-inhibited plasma of locally advanced/metastatic breast cancer patients, significantly elevated TGF-beta (1) was observed (median value: 65.5 ng/mL), which included untreated and previously treated patients with median values of: 74.2 ng/mL and 58.1 ng/mL, respectively. These findings indicate to the potential usefulness of this plasma marker in breast cancer prognosis, thus deserving future clinical attention
