The present invention provides compositions and methods for treating cancer or a metastasis thereof in a subject. In some embodiments, the methods involve administering a composition comprising therapeutically effective amount of at least one immune stimulator to the subject. In some embodiments, a combination of at least two immune stimulators is used for the treatment. In some embodiments, the combination includes an alpha thymosin peptide and an additional immune stimulator, and/or optionally one or more additional anti-cancer agents.