Plasma levels and tissue expression of soluble TGF[beta]rIII receptor in women with early-stage breast cancer and in healthy women: a prospective observational study

Background Mammary carcinogenesis is partly regulated by the transforming growth factor beta (TGF[beta]) signaling pathway. Its function in cancer progression and metastasis is highly dependent on disease stage, and it is likely modulated by the ratio of membrane-bound vs. soluble TGF[beta]rIII (sTGF[beta]rIII). In this prospective observational study, we assessed tissue expression and plasma levels of sTGF[beta]rIII in healthy women, women with benign breast lesions and in early-stage breast cancer patients. Methods In a preliminary study, plasma sTGF[beta]rIII levels were determined in 13 healthy women (age 19-40 years) at different phases of the ovarian cycle, and in 15 patients (age 35-75 years) at different times of the day. The main study assessed plasma concentrations of sTGF[beta]rIII in: (i) 158 healthy women in whom breast lesions were excluded; (ii) 65 women with benign breast lesions; (iii) 147 women with newly diagnosed breast cancer classified as American Joint Committee on Cancer (AJCC) stages 0 to IIB. Completers provided blood samples before surgery and at 10-30 and 160-180 days after surgery. Plasma sTGF[beta]rIII concentrations were determined using an indirect ELISA kit. Part of the removed tissues underwent immunohistochemical (IHC) staining and analysis of tissue TGF[beta]rIII expression. Results There appeared no relevant variations in plasma sTGFssrIII levels at different times of the day or different ovarian cycle phases. Before surgery, breast cancer patients had somewhat higher sTGF[beta]rIII than healthy women, or those with benign breast lesions (by 14.5 and 26 ng/mL, respectively), with a tendency of larger differences at higher age. This correlated with lower expression of TGF[beta]rIII in breast cancer vs. healthy tissue samples. At 160-180 days after surgery, plasma sTGF[beta]rIII levels in breast cancer patients declined by 23-26 ng/mL. Conclusions Plasma sTGF[beta]rIII levels do not seem to relevantly vary during the day or the ovarian cycle. The coinciding higher plasma levels in newly diagnosed cancer patients than in healthy subjects and lower TGF[beta]rIII expression in the malignant than in healthy breast tissue suggest ectodomain shedding as a source of circulating sTGF[beta]rIII. Decline in plasma levels after tumor removal supports such a view. Keywords: Soluble TGFssrIII, Betaglycan, Breast cancer, Shedding