We investigate the reflectivity spectra of photonic crystal cavities using the polarization of the incoming exciting light to tune the Fano interference between the radiation reflected by the polarized cavity mode and the light scattered by the photonic crystal pattern. The reflectivity is controlled by the polarization of the incident radiation, with the change from symmetrical to asymmetrical lineshapes well described by the Fano resonance formula. We use the scattering matrix formalism to obtain the reflectivity lineshapes by relating the electromagnetic field incident on the cavity to the radiation that is reflected in qualitative good agreement with the experimental results.