“…We used multicolor stainings to study the stem cell markers p63 [32][33][34][35][36][37][38], K5, and K14 [1,39], the differentiation markers and luminal keratins K18, K8/18, and K19 [1,[40][41][42][43][44][45][46], and the myoepithelial lineage markers smooth muscle actin (SMA) [47,48], smooth muscle myosin heavy chain [49], calponin [50,51], and CD10 [47,[52][53][54][55]. We also evaluated the functional markers estrogen receptor (ER)-alpha [5,23,29,[56][57][58][59][60][61] and Ki67 [62][63][64][65][66]. Based on our findings, we propose a modified concept of the cellular hierarchy of human breast epithelium, including K5+ luminal lineage progenitor cells in the ductal-lobular axis and p63+K5+ progenitor cells confined to nipple ducts.…”