ALDH1A1 and neoplasm: Histologic evaluation of 12 direct xenografts established from 11 different patient tumors (one xenograft was derived from a lymph node metastasis from the same patient in which a xenograft was derived from a primary tumor) identified a subset cells that strongly express ALDH1 relative to all other tumor cells in all but one specimen (four examples are shown in Figure 3B).