Tumor response to treatment is associated with increased frequency and resistance of CICs. (A) Cell growth of CICs and non-CICs from two independent human specimens was assessed by ATP based assay (CellTiter-Glo) following chemotherapy (FOLFOX: 50 µg/ml 5-flurouracil + 10 µM oxaliplatin + 1 µM leucovorin). Data are presented as mean ± SD (n = 3); **, P < 0.01; ***, P < 0.001. Student’s t test was used to assess the significance. The experiment was performed three times and representative data are shown. (B) Apoptosis of CICs and non-CICs from two independent human specimens was assessed by caspase 3/7 activation after chemotherapy. Data are presented as mean ± SD (n = 3); **, P < 0.01. Student’s t test was used to assess the significance. The experiment was performed three times and representative data are shown. (C) Enrichment of CICs in bulk cells from four independent human specimens was assessed by FACS analysis for CD44 (representative sample) after chemotherapy. Student’s t test was used to assess the significance. The experiment was performed once for each individual specimen.