Conventional dielectrophoresis (DEP) force on cell and particle is altered in the proximity of the electrodes due to the failure of the dipole approximation. In these conditions an anomalous DEP (aDEP) force rules the particle manipulation. Anyhow, the role of the aDEP is barely considered in the design of DEP devices. Here we analyze, using a multiscale simulation approach, the aDEP effects in micro-fluidic device coupled with interdigitated channel commonly used in continuous mode field flow fractionation dielectrophoretic (FFF-DEP) devices for the separation of circulating tumor cells (MDA) and Lymphocytes (LYM). We study the propagation of an injected density of MDA and LYM respectively and evaluate how the aDEP changes the migrations of the cells.