Abstract
Wnt-5a protein expression in primary tumors from unselected breast cancer patients has revealed a tumor suppressive function of the protein. However, in vitro experiments on human breast cancer cells have reported contradictory results, indicating both a tumor suppressive and promoting functions of Wnt-5a. This could be due to various functions of Wnt-5a in different subgroups of patients. The unselected cohorts analyzed to date for Wnt-5a protein expression contained few premenopausal patients. The aim of the present investigation was to evaluate the prognostic significance of Wnt-5a protein expression in a cohort of premenopausal women with comprehensive data on biomarkers, molecular subtypes and long-term outcome. In a randomized trial of adjuvant tamoxifen versus no adjuvant treatment, 564 premenopausal primary breast cancer patients were included. The median follow-up time was 14 years. A tumor tissue array was constructed and 361 samples were evaluated for Wnt-5a reactivity by immunohistochemistry. The primary end-point was recurrence-free survival. Wnt-5a protein expression was reduced or lost in 146/361 of tumors and correlated to younger age, estrogen receptor (ER) negativity and triple-negative phenotype. Wnt-5a was a prognostic factor in the whole cohort (p = 0.003). In patients with ER-positive tumors, Wnt-5a was an independent positive prognostic marker (HR 0.51 95% CI: 0.33-0.78 p = 0.002) and HER2 a negative prognostic marker (HR 2.84 95% CI: 1.51-5.31, p = 0.001) in a Cox multivariate analysis adjusted for standard prognostic markers and tamoxifen treatment. In the ER-negative subset, Wnt-5a added no prognostic information. In a subgroup analysis, Wnt-5a was significantly associated with better prognosis in patients with Luminal A tumors (p = 0.04). Conclusively, our results suggest that loss of Wnt-5a is a valuable prognostic marker in premenopausal breast cancer patients in particular in patients with ER-positive tumors and out-performed conventional prognostic factors in this subset of patients.