Crystalline polymorphs of Rigosertib sodium

A crystalline Form E of Rigosertib Sodium, characterized by data selected from one or more of the following:

• a) an XRPD pattern having peaks at 10.8, 11.9, 14.3, 18.7 and 19.3 degrees 2-theta±0.2 degrees 2-theta;
• b) an XRPD pattern as depicted in FIG. 5;
• c) a solid state 13C NMR spectrum having peaks at 175.0, 146.9, 145.4, 121.6 and 102.8 ppm=0.2 ppm;
• d) a solid state 13C NMR spectrum having the following chemical shift absolute differences from a reference peak at 101.5 ppm±2 ppm of 73.5, 45.4, 43.9, 20.1 and 1.3 ppm±0.1 ppm;
• e) a solid state 13C NMR spectrum as depicted in FIG. 10, 11, or 12;
• and
• f) a combination of any one or more of (a), (b), (c), (d) and (e).