Insulin-like growth factor-I (IGF-I) is thought to have antiapoptotic and mitogenic properties in colorectal cancer, whereas IGF-binding protein-3 (IGFBP-3) seems to exert a pro-apoptotic effect. Additionally, matrix metalloproteinase-7 (MMP-7), an enzyme with in vitro ability to degrade IGFBP-3, has been shown to be a prognostic factor in advanced colorectal cancer (ACRC). We studied whether chemotherapy treatment for ACRC modulates IGF-I, IGFBP-3, and MMP-7 serum levels. In 41 patients undergoing first-line therapy for ACRC, serum levels of IGF-I, IGFBP-3, and MMP-7 were measured with immunoassays at baseline and every 3 months until progressive disease, or a maximum of five determinations, during a chemotherapy regimen of either FOLFOX or FOLFIRI therapies. Associations were assessed for paired samples, using t-test or Wilcoxon ranks test depending on normality of the variable, verified with Shapiro-Wilk test. An average of four extractions (range 3-5) were done, for a total of 157 determinations. Mean pretreatment values of IGF-I, IGFBP-3, and MMP-7 were 83 (95% CI, 73-92) ng/ml, 2372 (95% CI, 2121-2623) ng/ml, and 10.6 (95% CI, 7.21-13.98) ng/ml respectively. No significant changes in IGF-I were found, but a significant increase in IGFBP-3 serum concentrations was observed during or after chemotherapy treatment without progressive disease, compared with basal levels (P<0.001). A significant decrease in IGFBP-3 to 1983 ng/ml (95% CI, 1675-2292) and a significant increase in MMP-7 levels to 14.6 (7.6-21.7) ng/ml were observed at progression of disease compared with baseline and treatment levels (P<0.001). This study shows that IGFBP-3 and MMP-7 serum levels change during chemotherapy treatment. The increased MMP-7 levels at disease progression support the hypothesis that this protease could play a role in acquired resistance by degrading IGFBP-3.