ALDH1A1 and breast cancer: The Aldefluor assay, which permits investigators to detect and separate ALDH1-expressing cells from cells that lack ALDH1 expression, has led to a wave of cancer studies that have implicated ALDH1 in drug resistance of adenocarcinoma of lung [28], melanoma [29], breast cancer [30] and hematopoietic tumors, such as myeloma [8, 10].