In this paper, a method for enhancing the contrast of mammogram images based on the design of a nonlinear polynomial filter is presented. Mammograms suffer from low contrast and also basic contrast enhancing techniques such as Histogram Equalization and its modifications, which have good performance against natural images- are challenged when faced with mammograms. Because increasing the contrast of medical images such as mammograms leads to saturation in bright regions and weakens marginal pattern of tumor. In this work, the design of non-linear filter is done such that shape of the potential tumor -that plays an important role in diagnosing it- are preserved. In this paper, unlike other methods, the nonlinear filter coefficients are adjusted to each input image through a support of the well-known contrast enhancement algorithm, i.e. CLAHE. Quantitative and qualitative evaluations of this method in various experiments and on several images from MIAS dataset show that the proposed method has acceptable performance.