Apalumide is a small molecule androgen receptor (AR) antagonist with potential anti-tumor activity. Apalumide binds to AR in the target tissue, preventing androgen induced receptor activation and promoting the formation of inactive complexes that cannot be transferred to the nucleus. This prevents the binding and transcription of AR responsive genes. This ultimately inhibits the expression of genes that regulate prostate cancer cell proliferation and may lead to inhibition of cell growth in AR expressing tumor cells.