CRF affected proliferation and apoptosis of MCF7 cells in a time dependent manner. Cells were stimulated with 10-8 M CRF or vehicle (control) for 24, 48, and 72 hours, and cell growth was measured using the MTT assay (A); apoptosis was measured by the ApoPercentage Assay (B). CRF significantly suppressed proliferation at all time points tested and apoptosis 48 hours after CRF stimulation. Data are expressed as % of control (unstimulated cells). Results represent the average of 4 independent experiments where each condition was assayed in triplicate. *p < 0.05; **p < 0.01 compared to control cells at the same time point.