The effect of anti-CK MAb on cell cycle (A) and proliferation (B) of breast tumor cells cultured on fibronectin. MCF-10A neoT and MCF-7 cells were cultured in serum-free medium in the absence or presence of anti-CK MAb. After 24 h they were harvested and analyzed for cell cycle status by flow cytometry. The percentage of anti-CK MAb treated and untreated cells in S phase is given (A, top). The representative histogram used to determine the percentage of distinctive cell populations is shown at the bottom. For the proliferation assay, MCF-7 cells were labeled with CFSE reagent and cultured for 48 h in the presence or absence of anti-CK MAb. Proliferation threshold was set according to CFSE labeled cells analyzed immediately after labeling (B, bottom). The percentage of proliferating cells of the PIneg population is given (B, top). Results represent at least three independent assays. P values of < 0.05 are marked with *, and P values < 0.001 with **.