AR and breast cancer: However, identifying exact percentages of AR expression among the various breast cancers—HR-positive, HER2-positive, or triple negative breast cancer (TNBC)—is somewhat challenging due to considerable variability in methodology, including differing locations of expression (cytoplasmic versus nuclear), cut off points for immunohistochemical (IHC) receptor expression (≥1%, ≥5% or ≥10%), and the antibody used in staining.