Unresectable metastatic colorectal cancer patient cured with cetuximab-based chemotherapy: a case report with new molecular insights.

Here we report the case of a 20-year-old patient who was diagnosed in 2002 with a metastatic colorectal cancer (CRC). He achieved a complete response under cetuximab-based therapy and remains without disease recurrence until now while chemotherapy was discontinued in 2009. The tumor exhibited high level of epidermal growth factor receptor (EGFR) amplification, no mutation in KRAS, NRAS or BRAF genes and a microsatellite-stable (MSS) phenotype. Intriguingly this young patient was carrying a monoallelic germline mutation of MUTYH that was associated with an inactivation of the second allele by loss of heterozygosity on tumor DNA. Moreover, this mutation was associated with a specific mutational signature on tumor level characterized by C > A single base substitutions and a higher mutational load than usually observed in MSS neoplasms. This case report paves the way for further researches on MUTYH-associated cancers' sensitivity to anticancer therapies.