CD44 and ductal breast carcinoma in situ: A population of CD44+/ALDH1+/Ki67− cancer ‘stem cells’ has been previously described in patients with DCIS at a frequency of 0.36–15% using triple immunohistochemistry.9 Using flow cytometry, the same group found the frequency of CD44+/CD24−/CK+/CD45− cells in DCIS ranges from 2.6–18%.10 However, Ki67low, AKT1low QCCs do not clearly express the marker profile ascribed to cancer ‘stem cells’ e.g., CD44high/CD24low 4.