Genome-wide association studies (GWAS) have been used in cancer research in the last two decades, contributing to significant advances in the understanding of many cancers. Protein association studies (PWAS) may provide more insight into the mechanisms of cancer and improve cancer prediction. We focus on seven phenotypes of breast, endometrial, ovarian, and prostate cancers, using previously-built protein prediction models to find proteins that are significantly associated with these cancers.