ena-STUDY-Candiolo Cancer Institute-28-04-2015-15:59:11:152-47
Clonal evolution and resistance to EGFR blockage in the blood of colorectal cancer patients
Colorectal cancer (CRC) is a genetic disease governed by clonal evolution. Genotyping CRC tissue is routinely employed for therapeutic purposes but this approach has significant limitations. A tissue sample represents a single snapshot in time, is subjected to selection bias due to tumor heterogeneity, and can be difficult to obtain. We exploited circulating DNA to genotype colorectal tumors and track clonal evolution during therapies with the anti- EGFR antibodies cetuximab or panitumumab. We found that RAS pathway mutations, which are evaluated before administration of EGFR blockade, can be ascertained directly in the blood. Sequencing of circulating DNA identified genomic alterations in KRAS, NRAS, MET, ERBB2, FLT3, and MAP2K1 in patients with primary or acquired resistance to EGFR blockade. Secondary resistance is frequently accompanied by emergence of mutant RAS clones, which can be tracked in blood. Upon withdrawal of anti-EGFR antibodies, KRAS alleles decline in circulating DNA indicating that clonal evolution continues beyond clinical progression. Functional analysis of CRC cells, which had acquired resistance to cetuximab, revealed that upon antibody withdrawal KRAS clones decay, while the population regains drug sensitivity. In a clinical case, we document that when KRAS declines in blood, rechallenging with anti-EGFR antibodies is clinically effective. These results establish proof of principle that genotyping CRCs using circulating DNA can inform therapeutic decisions, identify mechanisms of drug resistance and provide insights for further lines of therapy.
Colorectal cancer (CRC) is a genetic disease governed by clonal evolution. Genotyping CRC tissue is routinely employed for therapeutic purposes but this approach has significant limitations. A tissue sample represents a single snapshot in time, is subjected to selection bias due to tumor heterogeneity, and can be difficult to obtain. We exploited circulating DNA to genotype colorectal tumors and track clonal evolution during therapies with the anti- EGFR antibodies cetuximab or panitumumab. We found that RAS pathway mutations, which are evaluated before administration of EGFR blockade, can be ascertained directly in the blood. Sequencing of circulating DNA identified genomic alterations in KRAS, NRAS, MET, ERBB2, FLT3, and MAP2K1 in patients with primary or acquired resistance to EGFR blockade. Secondary resistance is frequently accompanied by emergence of mutant RAS clones, which can be tracked in blood. Upon withdrawal of anti-EGFR antibodies, KRAS alleles decline in circulating DNA indicating that clonal evolution continues beyond clinical progression. Functional analysis of CRC cells, which had acquired resistance to cetuximab, revealed that upon antibody withdrawal KRAS clones decay, while the population regains drug sensitivity. In a clinical case, we document that when KRAS declines in blood, rechallenging with anti-EGFR antibodies is clinically effective. These results establish proof of principle that genotyping CRCs using circulating DNA can inform therapeutic decisions, identify mechanisms of drug resistance and provide insights for further lines of therapy.