Insulin‐like growth factor 1 expression correlates with clinical outcome in K‐RAS wild type colorectal cancer patients treated with cetuximab and irinotecan

Seventy to 40% of K‐RAS wild type colorectal tumors does not seem to benefit from treatment with antiepidermal growth factor receptor (anti‐EGFR) monoclonal antibodies. Recent data suggested that in presence of IGF‐1 system, altered activation colorectal cancer cells may escape anti‐EGFR mediated cell death. The interaction between IGF‐1 expression and K‐RAS mutational analysis was tested to verify the ability of IGF‐1 to identify a subgroup of patients more likely to benefit from EGFR‐targeted antibodies treatment. IGF‐1 expression and K‐RAS mutational status was assessed in advanced colorectal cancer patients receiving irinotecan/cetuximab. One hundred twelve patients were analyzed. IGF‐1 was negative in 30 patients (27%) and overexpressed in the remaining 82 cases (73%). In IGF‐1 negative and IGF‐1 positive tumors, we observed progressive disease in 9 (30%) and 55 (67%) patients, respectively (p = 0.001). Median progression‐free survival was 7.5 mo in patients showing IGF‐1 negative tumors and 3 mo for IGF‐1 expressing tumors (p = 0.002). Among K‐RAS wild type patients, IGF‐1 negative and positive tumors showed a partial response to cetuximab‐irinotecan in 13 (65%) and 11 (22%) cases, respectively (p = 0.002). Median progression‐free survival in IGF‐1 negative tumors was 10 mo and 3.2 mo in IGF‐1 positive colorectal cancers (p = 0.02). IGF‐1 proved to be a possible predictive factor for resistance to anti‐EGFR monoclonal antibodies in K‐RAS wild type colorectal cancer. Combined IGF‐1 and K‐RAS analysis may represent an effective strategy for a better selection of responding colorectal cancer patients.