Soluble epidermal growth factor receptors 2 and 3 (HER2 and HER3) splice variant proteins with HER2 and HER3 antagonist activity and anti-proliferative properties, as well as the corresponding nucleic acids, are provided for treatment of proliferative diseases, in particular cancer. Also provided are compositions and methods for inducing expression of these splice variants, including splice switching oligonucleotides that modulate splicing of pre-mRNA that codes for these receptors.