Diagnosis and treatment of human epidermal growth factor receptor 2-positive metastatic colorectal cancer: a systematic literature review

Human epidermal growth factor receptor 2 (HER2)-targeted therapies have been investigated for therapeutic benefit in RAS / BRAF wild-type/HER2+ metastatic colorectal cancer (mCRC). Unlike HER2+ breast and gastric cancer, there are no regulatory criteria for determining HER2 overexpression in patients with mCRC. This systematic literature review describes unmet needs for patients with HER2+ mCRC in relation to testing and treatment, highlights the importance of early HER2 testing at mCRC diagnosis, and discusses the evolving treatment landscape. We utilised PubMed and EMBASE databases up to November 2023 to identify journal articles and published congress abstracts relating to the HER2+ disease and treatment landscape, HER2 testing in mCRC, and HER2-targeted treatments in mCRC. Many studies have demonstrated the utility of immunohistochemistry, in situ hybridisation, and next-generation sequencing (tissue- and circulating tumour DNA-based) for detecting HER2 overexpression/amplification in mCRC and have attempted to establish consolidated criteria like those used for breast and gastric cancer. The value of HER2-targeted treatments in patients with HER2+ mCRC has been evidenced by clinical trials and meta-analyses, with strong evidence from MOUNTAINEER and DESTINY-CRC01 which supports the use of tucatinib + trastuzumab or trastuzumab deruxtecan, respectively, among this patient population. However, real-world analyses have confirmed that patients with HER2+ mCRC are not routinely tested for HER2 overexpression. Strong evidence and clinical guidelines support the value of HER2-targeted treatment among patients with HER2+ mCRC. There is a need for increased awareness and earlier uptake of HER2 testing among patients with mCRC to broaden treatment options and optimise outcomes for this patient population.