A fumarate salt and a maleate salt of compound (I) represented by the following structural formula, as well as their corresponding pharmaceutical compositions, are disclosed. Particular single crystalline forms of 1:1 compound (I) fumarate and 1:1 compound (I) maleate are characterized by a variety of properties and physical measurements. Methods of preparing specific crystalline forms of 1:1 compound (I) fumarate and 1:1 compound (I) maleate are also disclosed. The present invention also provides methods of treating a subject with a cancer.