SUMMARY: ColoRectal Cancer (CRC) is the third most common cancer diagnosed in both men and women in the United States. The American Cancer Society estimates that approximately 154,270 new cases of CRC will be diagnosed in the United States in 2025 and about 52,900 patients will die of the disease. The lifetime risk of developing CRC is about 1 in 23.
It is estimated that approximately 30% of patients with Stage II or III CRC and 60-70% of patients after oligometastatic resection experience recurrence. Adjuvant chemotherapy for patients with resected, locally advanced, node-positive (Stage III) colon cancer has been the standard of care since the 1990s. However, not all patients with Stage III disease benefit from adjuvant chemotherapy. In the IDEA trial, the absolute Disease Free Survival benefit of adjuvant chemotherapy for the lowest-risk Stage III group and the highest-risk group was 8% and 20%, respectively, suggesting that a substantial number of patients with low-risk Stage III cancer can safely forgo adjuvant chemotherapy or be considered for treatment de-escalation. Even though 80% of patients with Stage II colon cancer are cured with surgery alone, adjuvant chemotherapy is recommended for patients who have Stage II colon cancer with high-risk clinicopathological features, including tumor penetration of the serosa (T4 disease). However, the benefit of adjuvant chemotherapy for patients with Stage II disease remains unclear, with less than 5% of patients benefiting from adjuvant chemotherapy. There is therefore an unmet need for more precise markers to predict risk of recurrence after surgery for resectable colon cancer, other than clinicopathological risk factors, and thus avoid exposure to unnecessary chemotherapy.
Circulating Tumor DNA (ctDNA) refers to DNA molecules that circulate in the bloodstream after cell apoptosis or necrosis, and can be detected in the cell-free component of peripheral blood samples (Liquid Biopsy) in almost all patients with advanced solid tumors including advanced CRC. ctDNA is a valuable biomarker and is directly evaluated for evidence of Minimal Residual Disease and allows early detection of relapse. Several studies have shown that detectable ctDNA following curative intent surgery for early stage cancers, including those with Stage II colon cancer, is associated with a very high risk of recurrence (more than 80%) without further adjuvant therapy. It has remained unclear whether adjuvant treatment is beneficial for these ctDNA-positive patients who are at high risk for recurrence.
The BESPOKE CRC trial is a multicenter, prospective, observational study, designed to evaluate the role of Natera’s SIGNATERA® assay in informing adjuvant chemotherapy decisions for patients with surgically resected pathologic Stage II and III Colorectal Cancer (CRC). SIGNATERA® test is a personalized, tumor-informed ctDNA (circulating tumor DNA) assay for tracking 16 tumor-specific mutations in the blood for Minimal Residual Disease (MRD) determination and molecular monitoring. This study aimed to assess whether ctDNA could improve the decision-making process for adjuvant chemotherapy, thereby influencing the course of treatment and ultimately, patient outcomes.
This study included 1780 patients who had undergone surgical resection for Stage II or III CRC. These patients were enrolled in the study and were followed for their ctDNA status at various time points after their resection. The first ctDNA sample was taken for MRD 2 to 6 weeks following surgery (MRD time point). Subsequent samples were collected at 2, 4, and 6 months, and then every 3 months up to 24 months after resection. The surveillance ctDNA collection started at 6 months or later from surgical resection. The treating oncologists were provided with the ctDNA results of their patients and were allowed to base treatment decisions on these findings, within the context of standard-of-care guidelines. After exclusions, 1166 patients remained in the final analysis, 694 patients in the adjuvant chemotherapy cohort and 472 patients in the observation cohort. The median age of the study participants was 61.8 years, majority of the patients were male (56.7%), most patients had stage III CRC (55.7%), 59.5% of patients received adjuvant chemotherapy, while 83.9% of the participants did not experience a recurrence during the study period. The Primary endpoint of this study was to evaluate the impact of ctDNA testing on adjuvant treatment decisions, as well as the rates of asymptomatic CRC recurrences. Secondary endpoints included the MRD clearance rate, survival rates of MRD-negative patients, Overall Survival, and Patient-Reported Outcomes. The median follow-up was 23.9 months
ctDNA and Disease-Free Survival (DFS)
The study found that postoperative ctDNA positivity was a strong predictor of inferior Disease-Free Survival (DFS) in patients with both Stage II and III disease. At the MRD time point (first ctDNA sample 2-6 weeks post surgery), 7.54% of patients with Stage II disease (N= 517) tested positive for MRD versus 28.35% of patients with Stage III disease (N= 649). These findings were crucial for determining which patients might be at higher risk of recurrence.
- Among Stage II patients, those with positive postoperative ctDNA had a significantly lower 2-year DFS rate of 45.9%, compared to 91.8% in ctDNA-negative patients (HR=11.23; P <0.0001).
- Among Stage III patients, those with positive ctDNA were also associated with poorer DFS, with a 2-year DFS rate of 35.5% versus 87.4% for ctDNA-negative patients (HR=8.33; P <0.0001).
Further analyses showed that positive ctDNA at the first surveillance time point was linked with an inferior DFS (HR=20.63; P <0.0001). Patients who became positive for ctDNA at any time during surveillance had a 26.4-times higher risk of recurrence compared to those who remained ctDNA-negative.
ctDNA Clearance and Treatment Efficacy
One of the most compelling findings of the study was the correlation between ctDNA clearance during and after adjuvant chemotherapy and improved DFS. Patients whose ctDNA was cleared during treatment had significantly better outcomes:
- Hazard ratio for DFS at 3 months after chemotherapy: 0.43 (P <.0001)
- Hazard ratio for DFS at 6 months: 0.31 (P <.0001)
These results suggest that ctDNA clearance could be a powerful marker for assessing the effectiveness of adjuvant chemotherapy, reinforcing its potential as a treatment monitoring tool.
Recurrence Detection and Metastasis-Directed Therapy
The ctDNA test demonstrated high sensitivity in detecting disease recurrence, particularly in the liver, which had the highest sensitivity at 96%. It also showed high sensitivities in detecting recurrences in low-shedding sites like the lung (76%) and peritoneum (79%). Bone and abdominal wall recurrences had a sensitivity of 100%, though the small number of such cases limits the ability to draw firm conclusions.
Of the 188 patients who experienced disease recurrence, 86% had a prior positive ctDNA test. Notably, 30% of those patients received metastasis-directed therapy, with 81% of them undergoing surgical intervention. This emphasizes the potential of serial ctDNA monitoring in improving early detection of recurrences and facilitating more effective interventions, including metastasis-directed therapy, which could provide these patients with a chance for a cure.
Impact of Adjuvant Chemotherapy in MRD-Positive vs MRD-Negative Patients
The study also highlighted the differing effects of adjuvant chemotherapy in MRD-positive versus MRD-negative patients. While MRD-negative patients saw no significant difference in DFS regardless of whether they received chemotherapy or observation, MRD-positive patients showed a clear benefit from adjuvant chemotherapy:
- 2-year DFS rates for MRD-positive patients was 40.3% with chemotherapy versus 24.7% with observation (HR=0.48; P =0.0008).
- 2-year DFS rates for MRD-negative patients was 89.7% with chemotherapy versus 89.5% with observation (HR=0.93; P =0.03).
These results underscore the potential of using ctDNA as a tool to help personalize treatment strategies, offering chemotherapy to those who are most likely to benefit (MRD-positive patients) and sparing others from unnecessary treatment.
Summary of Key Findings
- Tumor-informed ctDNA assays had a significant impact on adjuvant treatment decisions, influencing chemotherapy de-escalation in 16.3% of Stage II/III CRC cases.
- Postoperative ctDNA positivity correlated with inferior DFS, making it a strong prognostic tool for identifying high-risk patients.
- ctDNA clearance during and after chemotherapy was associated with improved DFS, highlighting its potential to monitor treatment efficacy.
- ctDNA assays demonstrated high sensitivity in detecting recurrences, particularly in the liver, and influenced the use of metastasis-directed therapy.
- Adjuvant chemotherapy showed a clear benefit in MRD-positive patients, further solidifying the role of this assay in personalizing treatment strategies for CRC patients.
This trial positions ctDNA as a pivotal tool in managing CRC, not only as a prognostic marker but also as a means to optimize treatment and improve patient outcomes.
Circulating tumor DNA for detection of molecular residual disease (MRD) in patients (pts) with stage II/III colorectal cancer (CRC): final analysis of the BESPOKE CRC sub-cohort. Shah P, Aushev V, Ensor J, et al. J Clin Oncol. 2025;43(suppl 4):15. doi:10.1200/JCO.2025.43.4_suppl.15
