The present invention relates to maleate salt forms of (E)-N-{4-[3-chloro-4-(2-pyridinylmethoxy]anilino}-3-cyano-7-ethoxy-6-quinolinyl}-4-(dimethylamino)-2-butenamide, methods of preparing crystalline maleate salt forms, the associated compounds, and pharmaceutical compositions containing the same. The maleate salts are useful in treating cancers, particularly those affected by kinases of the epidermal growth factor receptor family.