AR and prostate cancer: Mechanistically, patients harboring isoform BRAF3-9 (Δ exons 4–8) or BRAF2-6 (Δ exons 3–5) that could eliminate RAS-binding domains often develop drug resistance.27,28 Advanced prostate cancer is commonly treated with drugs that inhibit androgen biosynthesis or antagonize the interaction between androgen and androgen receptor (AR).