Cancer-associated fibroblasts (CAFs) express epidermal growth factor receptor (EGFR), but are not sensitive to EGFR inhibition. (A) Immunofluorescence stained colorectal cancer tissue from a biopsy of patient 12620 displayed expression of EGFR (red) and αSMA (green). Full tissue slice is shown on top (scale bar: 5 mm), with a 20× zoomed-in section shown below (scale bar: 100 μm). (B) Quantitative polymerase chain reaction (qPCR) analysis of CAF-associated markers alpha-smooth muscle actin (αSMA), fibronectin (FN1), and vimentin (VIM) was performed on primary cultured CAFs (isolated from colorectal cancer (CRC) tissues of patients 12,905, 12,911, 13,000), normal primary fibroblasts (NCF12737) and CRC tumor cells (LIM1215). (C) Expression of EGFR in CAFs 12,905, 12,911, and 13,000 as detected by immunofluorescence. Scale bar: 100 μm. (D) Cells were treated with 1 μg/mL cetuximab (CTX) or IgG control for five days. Live and dead cell counts were obtained on days 0, 3, and 5 to calculate growth rates (cell doubling per hour), which were normalized to IgG condition for each cell type.