ALDH1A1 and ductal breast carcinoma in situ: They have found ALDH1 positive cells were more frequent in basal-like and HER2+ than in luminal tumors, but no significant difference of ALDH1 expression was observed in four histologic groups (invasive ductal carcinoma (IDC), IDC with ductal carcinoma in situ (DCIS), DCIS with microinvasion, and pure DCIS).