We propose a new model to simulate the growth of glioblastomas multiforma (GBM), the most aggressive glial tumors. This model relies upon an anatomical atlas including white fibers diffusion tensor information and the delineation of cerebral structures having a distinct response to the tumor aggression. We simulate both the invasion of the GBM in the brain parenchyma and its mechanical interaction (mass effect) with the invaded structures. The former effect is modeled with a reaction-diffusion equation while the latter is based on a linear elastic brain constitutive equation. In addition, we propose a new equation taking into account the mechanical influence of the tumor cells on the invaded tissues. This tumor growth model is assessed by comparing the virtual GBM growth with the real GBM growth observed between two MRIs of a patient acquired with six months difference.