Context: Breast cancer is the most common malignancy in women. Noninvasive biomarkers are needed for its early diagnosis and/or prognosis.Objective: The aim of this case-control study was the comparison of serum activins, follistatins, and members of the IGF family levels in women with benign vs malignant breast neoplasms vs apparently healthy controls.Design and Patients: Women with breast benign (n = 100) or malignant tumors (n = 145) and disease-free controls (n = 100) were recruited. Women with breast cancer were subsequently subdivided into recently diagnosed/treatment-naive (n = 112) and chemotherapy-treated (n = 33). Anthropometric, demographic, biochemical, and histological data were recorded.Setting: A breast cancer clinic in Thessaloniki, Greece.Main Outcome Measures: Serum levels of activin A, activin B, follistatin, follistatin-like (FSTL)-3, total IGF-1, total and intact insulin-like growth factor binding protein (IGFBP)-4 and pregnancy-associated plasma protein-A (PAPP-A) were measured with highly specific ELISA kits.Results: In adjusted comparisons, substantial differences in FSTL-3, total and intact IGFBP-4, PAPP-A, and total IGF-1 were observed between groups. In logistic regression analysis, primarily total IGFBP-4 levels were independently associated with the overall presence of breast malignancy. FSTL-3 was the only variable that could distinguish between a benign vs malignant breast mass. In linear regression analysis, FSTL-3 was independently associated with tumor size.Conclusions: We showed that members of the IGF-1/IGFBP-4/PAPP-A axis and FSTL-3 may serve as surrogate markers in breast cancer. Future mechanistic and longitudinal studies and/or clinical trials are needed to explore the efficacy of these molecules as noninvasive biomarkers and their possible therapeutic potential in breast cancer.