For thymidine incorporation studies, 30,000 HMEC-L/well were plated in a 24-well plate. Cells were allowed to attach and recover for 24 hours and were then placed in serum-free media and treated with SDF-1 (0.1 nM, 1 nM, 100 nM), long-R-IGF-1 (0.1 nM, 1 nM, 10 nM, 100 nM), VEGF (5 nM, 20 nM, 50 nM, 100 nM), or a combination of SDF and either IGF or VEGF. Full EBM2 media was used as a positive control for the cells. The cells were treated for 24 hours; this was followed by the addition of 40 μL of 0.1 mCi/mL [3H] thymidine (Perkin Elmer, Boston, MA) during the last 2 hours of incubation. The cells were washed twice with 10% trichloroacetic acid (Fisher Scientific, Austin, TX) and lysed with 0.2 N NaOH. One hundred microliters of the cell lysate was counted in a multipurpose scintillation counter (LS 6500; Beckman Coulter, Fullerton, CA).