The mouse monoclonal antibody p40 [BC28] recognizes an epitope unique to the p40 protein and may have applications in cases where p63 has traditionally been used. To date, p63 [4A4] has been a frequently used marker of basal epithelium in normal prostate, with expression not typically observed in prostatic adenocarcinoma. A study has shown p40 (M) antibody staining of normal prostate glands and prostatic intraepithelial neoplasia (PIN) equivalent to p63, with no p40 staining observed in prostate cancer. p63 [4A4] recognizes both the p63 and p40 proteins. In contrast to the rabbit polyclonal p40 antibody, p40 [BC28] does not stain macrophages.