Pharmaceutical compositions and single unit dosage forms of Compound A (3-(5-amino-2-methyl-4-oxo-4H-quinazolin-3-yl)-piperidine-2,6-dione), or an enantiomer or a mixture of enantiomers thereof, a pharmaceutically acceptable salt, solvate, hydrate, co-crystal, clathrate, or polymorph thereof, are provided herein. Also provided are methods of treating, managing, or preventing cancer using the dosage forms described herein.