Signatera ctDNA Assay Found to Influence Adjuvant Chemo Decision-Making in Stage II/III CRC

The use of a tumor-informed, personalized circulating tumor DNA (ctDNA) assay affected adjuvant treatment decisions in 16.3% of cases among patients with stage II/III colorectal cancer (CRC), according to final analysis data from the observational BESPOKE CRC (NCT04264702) subcohort presented at the 2025 Gastrointestinal Cancers Symposium.

Of those treatment changes, 59.9% resulted in chemotherapy treatment de-escalation and 35.7% resulted in chemotherapy intensification––4.4% of subsequent therapy decisions were not available. Notably, 13.2% of patients had metastatic disease diagnosed as a result of a positive postoperative ctDNA test.

Of the 83.7% of physicians who said the ctDNA result did not affect their treatment decision, 83.8% said it did make them feel more comfortable with their prior planned treatment vs 16.1% who claimed it did not affect their comfort level.

“In the largest multicenter ctDNA study reported in the United States, postoperative ctDNA testing led to a change in adjuvant management for 1 out of 6 patients and validated the adjuvant plan for most patients,” Purvi K. Shah, MD, lead study author and medical oncologist at Virginia Cancer Institute in Richmond, stated in a presentation of the data.

The current standard of care for patients with surgically resected, high-risk, stage II/III CRC is 3 to 6 months of adjuvant chemotherapy. However, only a subset of these patients will derive benefit from this treatment.

BESPOKE CRC is a multicenter, prospective, observational study evaluating whether Natera’s Signatera—a tumor-informed, personalized ctDNA assay—could inform adjuvant chemotherapy decision-making for patients with pathologic stage II/III CRC.

“In this prospective, observational study, ctDNA was collected from 1780 patients with surgically resected, stage II/III CRC at varying time points,” Shah explained. “The first time point, called the MRD time point, was collected 2 to 6 weeks after resection, and thereafter, collections occurred at 2, 4, and 6 months, and then every 3 months up to 24 months after resection. The surveillance time point collection started at 6 months or later from surgical resection. Treating oncologists received the results of the tests and were allowed to treat patients at their discretion per standard-of-care guidelines. They were prospectively surveyed at predetermined time points.”

Of the 1780 patients who were enrolled, 614 were excluded, leaving 1166 for inclusion in the final analysis. A total of 694 were included in the adjuvant chemotherapy cohort, and 472 were included in the observation cohort.

Baseline characteristics of the final analysis study population revealed that the median age was 61.8 years (range, 22-94) and most patients were male (56.7%). Most patients had pathologic stage III disease (55.7%), were under the age of 65 (57.8%), White (72.4%), and not Hispanic or Latino (82.0%). Most patients had an ECOG performance status of 0 (63.7%), received adjuvant chemotherapy (59.5%), and did not experience recurrence (83.9%).

Notably, at the MRD time point, 7.54% (95% CI, 5.57%-10.15%) of patients with stage II disease (n = 517) tested positive for MRD vs 28.35% (95% CI, 25.02%-31.94%) of patients with stage III disease (n = 649).

Median follow-up was 23.9 months (range, 0.5-36.5).

Additional results illustrated that postoperative ctDNA positivity predicted for inferior disease-free survival (DFS) regardless of whether patients had stage II or III disease. Among patients with stage II disease, the 2-year DFS rate was 45.9% (95% CI, 32.1%-65.8%) in those with ctDNA positivity vs 91.8% (95% CI, not evaluable [NE]-NE) in those with ctDNA negativity at the MRD time point (HR, 11.23; 95% CI, 6.43-19.62; P <.0001). For patients with stage III disease, the 2-year DFS rates were 35.5% (95% CI, 28.6%-44.2%) and 87.4% (95% CI, 83.8%-91.1%) in those with positive and negative ctDNA, respectively (HR, 8.33; 95% CI, 5.89-11.78; P <.0001).

Moreover, positive ctDNA at the first surveillance time point was associated with inferior DFS (HR, 20.63; 95% CI, 14.37-29.61; P <.0001). Investigators also conducted a time-dependent analysis for DFS during the surveillance period and showed that patients who became positive at any time point during surveillance had a 26.4-higher hazard of recurrence vs those who remained ctDNA negative (95% CI, 21.6-32.4; P <.0001).

Furthermore, ctDNA clearance during and after adjuvant chemotherapy was associated with improved DFS, with hazard ratios of 0.43 (95% CI, 0.29-0.64; P <.0001) and 0.31 (95% CI, 0.19-0.52; P <.0001) at months 3 and 6, respectively. “This reflects the test’s ability in demonstrating potential effectiveness of adjuvant chemotherapy,” Shah said.

The rates of ctDNA clearance by week 12, 20, month 6, and overall in patients with MRD positivity (n = 160) were 49.44% (95% CI, 42.2%-56.7%), 67.22% (95% CI, 60.1%-73.7%), 73.33% (95% CI, 66.4%-79.3%), and 75.56% (95% CI, 68.8%-81.3%), respectively.

Shah went on to explain that of the 188 patients whose disease recurred, 86% had a prior positive Signatera test. Of these, 30% of patients underwent metastasis-directed therapy (MDT), the most common of which was surgery in 81.04% of cases.

“This underscores the value of following ctDNA serially in the surveillance setting, not only as a prognostic marker, but for its potential ability to be associated with a higher rate of MDT compared to historical data, potentially giving these patients a shot at a cure,” Shah said.

With regard to recurrence, Shah stated, “The ctDNA test had a high sensitivity in detecting recurrences across a variety of different anatomical sites. The liver was the most common site of metastases and had the highest sensitivity of 96%. However, low-shedding sites such as the peritoneum and lung also had sensitivities as high as 79% and 76%, respectively. Although bone and abdominal wall recurrences had a high sensitivity of 100%, I would use caution in drawing inferences, since the actual number of occurrences in those sites were extremely small.”

Finally, the effect of adjuvant chemotherapy on MRD-positive and MRD-negative patients was assessed separately and showed a benefit evident only in MRD-positive patients. The 2-year DFS rates in MRD-positive patients were 40.3% (95% CI, 33.3%-48.9%) and 24.7% (95% CI, 13.2%-46.3%) with adjuvant chemotherapy and observation, respectively (HR, 0.48; 95% CI, 0.31-0.77; P =.0008). Among MRD-negative patients, the 2-year DFS rates were 89.7% (95% CI, 86.7%-92.9%) and 89.5% (95% CI, 86.2%-92.9%) with adjuvant chemotherapy and observation, respectively (HR, 0.93; 95% CI, 0.59-1.45; P =.0287).

“This highlights another potential value of utilizing a positive ctDNA test to select patients for adjuvant chemotherapy,” Shah stated.

Disclosures: Dr Shah shared no disclosures.

Reference

Shah P, Aushev V, Ensor J, et al. 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. J Clin Oncol. 2025;43(suppl 4):15. doi:10.1200/JCO.2025.43.4_suppl.15