PHLDA1 (Pleckstrin homology-like domain, family A, member 1), also known as TDAG51 (T-cell death-associated gene 51), is a follicular bulge stem cell marker that has been shown to be important and superior to CK20 in differentiating trichoepithelioma and basal cell carcinoma, especially in small skin biopsies [27,28]. This evidence concerns the gene KRT20 and basal cell carcinoma.