MRCP2-3596

A 50-year-old man presents with a recent history of weight loss and changes in bowel habits. Upon initial investigations, it is discovered that he has metastatic colorectal cancer with multiple liver metastases. The colorectal multidisciplinary team (MDT) determines that his liver metastasis is currently non-resectable and refers him to oncology for consideration of chemotherapy to downstage his disease in hopes of achieving surgical resection.

As part of his chemotherapy regimen, the oncology team considers combination therapy with cetuximab (Erbitux). To ensure successful treatment with cetuximab, which histopathological subtype is essential?