The present disclosure relates to a) crystalline forms of N—((R)-2,3-dihydroxypropoxy)-3,4-difluoro-2-(2-fluoro-4-iodo-phenylamino)-benzamide; b) pharmaceutical compositions comprising one or more crystalline forms of N—((R)-2,3-dihydroxypropoxy)-3,4-difluoro-2-(2-fluoro-4-iodo-phenylamino)-benzamide, and, optionally, one or more pharmaceutically acceptable carriers; c) methods of treating a tumor a cancer, or a Rasopathy disorder by administering one or more crystalline forms of N—((R)-2,3-dihydroxypropoxy)-3,4-difluoro-2-(2-fluoro-4-iodo-phenylamino)-benzamide to a subject in need thereof, and methods of producing essentially pure Form IV of N—((R)-2,3-dihydroxypropoxy)-3,4-difluoro-2-(2-fluoro-4-iodo-phenylamino)-benzamide.