Methods of reducing the likelihood of a cancer or precancer developing resistance to a cancer therapeutic or prevention agent are provided herein. The methods include administering the cancer therapeutic or prevention agent and a vaccine comprising a polynucleotide encoding a polypeptide whose expression or activation is correlated with development of resistance of the cancer or precancer to the cancer therapeutic or prevention agent to a subject. The vaccine may include a polynucleotide encoding an ESR1 polypeptide or a truncation, deletion or substitution mutant thereof. Methods of using the vaccine including the polynucleotide encoding the ESR1 polypeptide to treat a cancer or precancer are also provided.
