We investigate the role of polarization in sparse differential microwave imaging for the breast-cancer localization. We consider two types of antenna arrays, placed around realistic inhomogeneous breast models. In the first case, the antennas are vertical with respect to the chest wall, whereas in the second case, the antennas are located in the horizontal planes, parallel to the chest wall. In the approximate linear model, we use numerically computed three-dimensional (3-D) Green's functions, assuming that the breast tissue parameters are known from the previous measurements. By introducing some deviation in the permittivity of the breast tissues, we compare the estimation accuracy yielded by different array configurations and assess the robustness of the sparse approach.