This invention relates to a hydrochloride, malate, oxalate and tartrate salt forms of 1-(4-{1-[(E)-4-cyclohexyl-3-trifluoromethyl-benzyloxyimino]-ethyl}-2-ethyl-benzyl)-azetidine-3-carboxylic acid (Compound I), to pharmaceutical compositions comprising this salt, to processes for forming this salt and to its use in medical treatment. In addition, the present invention also relates to new polymorphic forms of each of these salts, as well as to pharmaceutical compositions comprising these polymorphic forms, to processes for obtaining them, and their use in medical treatment.