Tumor response to treatment is associated with increased frequency of CAFs. (A) Frozen sections of human colorectal tumors matched before and after cytotoxic treatment from a representative patient (334) were stained for markers of activated fibroblasts (Vimentin, αSMA) and epithelial cells (EpCAM). Nuclei stained with DAPI. Arrows indicate the stromal compartment. (B) Frozen sections of human colorectal tumors matched before and after cytotoxic treatment from two different patients (1086 or 5712) were stained for αSMA and EpCAM. The ratio of the αSMA-positive area versus the EpCAM-positive area was quantified and shown on the right. Data are presented as mean ± SD. *, P < 0.05. Student’s t test was used to assess the significance. Data are representative of three experimental repeats per group. (C) cDNA levels of markers of activated fibroblasts (Vimentin, α-SMA, and PDGFRα) were quantified by quantitative RT-PCR in patients untreated and treated (17 samples each group). Data are presented as mean ± SD; *, P < 0.05; ***, P < 0.001. Student’s t test was used to assess the significance. The experiment was performed three times and representative data are shown. (D) Single cell suspensions from dissociated patient colorectal tumor were sorted by FACS for the expression of PGDFRα-PE. The purity of the sorted population was checked after the sorting. (E) The PDGFRα⁺ isolated population was validated by positive immunostaining for CAF markers (αSMA-Vimentin-FSP1-FAP) and negative immunostaining for an epithelial marker (EpCAM). Bars: (A and E) 50 µm.