Colorectal cancer (CRC) remains one of the most prevalent and deadly cancers worldwide, with a significant number of cases presenting at an advanced stage. If not treated early, CRC can metastasize at nearby or distant organs increasing the mortality rates. Approximately 20% of CRC-related deaths are attributed to metastasis that is observed at the time of diagnosis (1).
Treatment options for metastatic CRC have evolved over the years. Therapeutic decisions are based on the patient’s overall health status, the molecular profile of the tumor, and the location of the primary tumor. Standard treatment approaches include chemotherapy, targeted therapy, immunotherapy, or a combination of these, tailored to maximize efficacy and minimize toxicity (2).
Approximately 50% of patients with metastatic CRC have tumors with wild-type RAS genes, which initially respond well to anti-EGFR drugs like cetuximab and panitumumab (3). However, during treatment, these tumors can develop resistance due to new mutations that arise in genes such as RAS and BRAF. This necessitates changing the treatment approach to other chemotherapy regimens, often combined with anti-VEGF antibodies (4). Following disease progression after this second-line therapy, a third-line treatment option involves re-challenging the tumor with an anti-EGFR agent (cetuximab or panitumumab). This approach is based on the hypothesis that RAS wild-type clones may undergo repopulation within the tumor during the interval of non-anti-EGFR therapy. However, the efficacy of this strategy is currently not well understood.
Aim of the study
This study, published in ESMO Gastrointestinal Oncology, evaluated the efficacy of anti-EGFR re-challenge with chemotherapy in metastatic RAS wild-type CRC (5). The investigation targeted patients who, despite an initial positive response to first-line anti-EGFR treatment, experienced disease progression and showed no benefit from second-line therapy. The study sought to determine whether a treatment-free interval could restore sensitivity to anti-EGFR agents by allowing RAS wild-type clones to repopulate the tumor. Additionally, the study aimed to assess whether liquid biopsy and tumor profiling could help predict which patients would respond to re-challenge therapy by detecting acquired RAS mutations and other resistance markers in real time. Molecular profiling was employed to guide patient selection and treatment optimization, to achieve optimal clinical results.
Methods
The study enrolled patients with metastatic CRC who met specific criteria, ensuring a homogenous study population. Among other criteria, all participants had RAS wild-type tumors, a key factor for anti-EGFR therapy response. They had also received two prior treatment lines: a first-line regimen that included an anti-EGFR agent (cetuximab or panitumumab) and yielded clinical benefit for at least three months, followed by a second-line regimen without anti-EGFR that led to disease progression. This specific treatment history was essential for the re-challenge hypothesis.
After enrolling, the patients received panitumumab, an anti-EGFR monoclonal antibody, in combination with standard chemotherapy regimens. The choice of chemotherapy (FOLFIRI, mFOLFOX6, or irinotecan) was left to the investigator, but it had to differ from the patient’s second-line regimen and to resemble their initial first-line treatment. During treatment, patients underwent regular monitoring for disease progression.
In addition, a significant component of the study was the integration of translational research to explore the molecular mechanisms of treatment response and resistance. First, genetic testing using next-generation sequencing (NGS) on tissue biopsy samples was performed to confirm patients had RAS wild-type tumors before starting anti-EGFR therapy. This baseline profiling ensured that only patients who were initially eligible for anti-EGFR treatment were included in the study. Furthermore, liquid biopsy was performed using the NeoThetis liquid biopsy test for therapy re-evaluation to detect newly acquired resistance mutations that traditional profiling could not capture in real-time. NeoThetis analyzed circulating tumor DNA (ctDNA) from plasma samples and identified genetic variants derived from the tumor that could lead to therapy resistance and cancer development. The combination of tissue-based and liquid biopsy genetic testing analysis provided a comprehensive molecular characterization of the tumors and allowed for the exploration of potential biomarkers that could predict treatment outcomes or elucidate mechanisms of resistance.
Results
The results of the study provided key insights into the efficacy and limitations of anti-EGFR re-challenge in metastatic RAS wild-type colorectal cancer. The study demonstrated a modest objective response rate (RR) of 13%, indicating that only a small proportion of patients experienced significant tumor shrinkage. However, the disease control rate (DCR), which includes patients who had stable disease, reached 52%, suggesting that over half of the participants derived some benefit from the treatment, even if it only led to moderate tumor reduction.
In terms of survival outcomes, the median progression-free survival (PFS) was 2.8 months, indicating that, on average, patients remained without disease progression for this period following treatment initiation. The median overall survival (OS) was 8.7 months, reflecting the total duration from the start of treatment until death. These results suggest that while anti-EGFR re-challenge may offer some disease control, its overall impact on extending patient survival is limited.
The study also identified similarities and differences between tissue biopsy and liquid biopsy in detecting genetic mutations in colorectal cancer. Both methods successfully identified key mutations, such as those in RAS, TP53, and APC. However, while tissue biopsy confirmed patients’ initial RAS wild-type status, liquid biopsy later detected newly acquired RAS mutations (KRAS and NRAS) before re-challenge in nearly 48% of patients, revealing tumor evolution over time. This highlights the dynamic nature of tumor genetics and the need for real-time mutation profiling before considering re-challenge therapy. Interestingly, patients who remained RAS wild-type at the time of re-challenge showed slightly better response rates (18.2% RR and 54.5% DCR), but the differences were not statistically significant, suggesting that additional resistance mechanisms beyond RAS mutations might influence treatment outcomes.
Conclusion
The study provides valuable insights into the evolving landscape of metastatic CRC treatment. While anti-EGFR re-challenge with chemotherapy demonstrated some clinical activity, its effectiveness remains limited, particularly in the presence of acquired RAS mutations. In addition, the integration of liquid biopsy into clinical practice represents a significant advancement, offering a real-time, non-invasive approach to monitoring tumor genetics and guiding treatment decisions. Moving forward, a more personalized approach leveraging liquid biopsy could improve patient outcomes and redefine third-line treatment strategies for metastatic CRC.
References
(1) Ilyas MIM. “Epidemiology of Stage IV Colorectal Cancer: Trends in the Incidence, Prevalence, Age Distribution, and Impact on Life Span.” Clin Colon Rectal Surg. 2023 Mar 15;37(2):57-61. doi: 10.1055/s-0043-1761447. PMID: 38322602; PMCID: PMC10843881. https://pmc.ncbi.nlm.nih.gov/articles/PMC10843881/
(2) “Treatment for metastatic colon cancer.” Memorial Sloan Kettering Cancer Center. https://www.mskcc.org/cancer-care/types/colon/treatment/metastases
(3) Saeed O, Lopez-Beltran A, Fisher KW et al. “RAS genes in colorectal carcinoma: pathogenesis, testing guidelines and treatment implications.” J Clin Pathol. 2019 Feb;72(2):135-139. doi: 10.1136/jclinpath-2018-205471. Epub 2018 Nov 13. PMID: 30425122. https://jcp.bmj.com/content/72/2/135.long
(4) Sartore-Bianchi A et al. “Circulating tumor DNA to guide rechallenge with panitumumab in metastatic colorectal cancer: the phase 2 CHRONOS trial.” Nat Med. 2022 Aug;28(8):1612-1618. doi: 10.1038/s41591-022-01886-0. Epub 2022 Aug 1. PMID: 35915157; PMCID: PMC9386661.
(5) Sgouros, J., et al. (2025). “Anti-EGFR re-challenge with chemotherapy in RAS wild-type advanced colorectal cancer (A-REPEAT study): efficacy and correlations with tissue and plasma genotyping.” ESMO Gastrointestinal Oncology, 7, 100120. https://doi.org/10.1016/j.esmogo.2024.100120
