This invention relates to polymorphs of (R)-3-[1-(2,6-Dichloro-3-fluoro-phenyl)-ethoxy]-5-(1-piperidin-4-yl-1H-pyrazol-4-yl)-pyridin-2-ylamine that are useful in the treatment of abnormal cell growth, such as cancer, in mammals. This invention also relates to compositions including such salts and polymorphs, and to methods of using such compositions in the treatment of abnormal cell growth in mammals, especially humans.