Representative immunohistochemical staining intensity of ALDH1 for patients with breast cancer. (A) ALDH1 negative (0) result, (B) ALDH1 positive (1+), (C) = ALDH1 positive (2+) and (D) ALDH1 positive (3+). Strong staining was also observed on the normal ducts (E) and tumor stroma in some cases (F). Only cytoplasmic staining in the invasive tumor component was considered for final analysis. ALDH1, aldehyde dehydrogenase-1.