Rapid Readout: ctDNA Dynamics and Clinical Outcomes in the Adjuvant Management of Colorectal Cancer (GALAXY Study)

Insight on the observational GALAXY study, which analyzed the relationship between circulating tumor DNA and clinical outcomes in the adjuvant management of colorectal cancer.


  • Circulating tumor DNA (ctDNA)–based molecular residual disease has the potential to select patients who may benefit more from standard-of-care adjuvant chemotherapy by accurately assessing recurrence-risk post-surgery and by evaluating adjuvant colon cancer therapy (ACT) efficacy.
  • CIRCULATE-Japan project is a large platform enrolling patients with clinical stage II–IV resectable colorectal cancer (CRC) to evaluate the clinical utility of ctDNA minimal residual disease analysis. The study comprises 1 observational (GALAXY study) and 2 randomized phase 3 trials (VEGA and ALTAIR trials).


  • The GALAXY study utilizes a personalized, tumor-informed ctDNA assay (Signatera bespoke multiplex polymerase chain reaction next-generation sequencing) based on whole-exome sequencing of tumor tissue and matched normal sample.
  • The blood samples are collected before surgery and 4, 12, 24, 36, 48, 72, and 96 weeks after surgery.
  • Investigators can receive the results of the ctDNA assay in a timely manner and consider patients for enrollment in associated interventional phase 3 trials, such as VEGA and ALTAIR.
  • Association of ctDNA dynamics with a short-term clinical outcome and ACT efficacy are being investigated.
  • Patients enrolled in VEGA and ALTAIR trials were excluded from this analysis.


  • Even with an extended follow-up time, post-op 4-week positivity was significantly associated with inferior disease-free survival (DFS), consistent with previous results.
  • 6- and 12-month DFS rates by ctDNA dynamics from post-op 4 to 12 weeks were significantly different between “positive to negative” and “positive to positive” groups with a hazard ratio of 15.8.
  • Among post-op 4-week ctDNA-positive patients, ACT was able to clear ctDNA in 68% of ctDNA-positive patients by post-op 24 weeks, and a 6-month DFS rate was significantly higher in patients with ACT vs without ACT across all stages.
  • 2 of 3 post-op 4-week ctDNA-positive patients even with stage I or low-risk stage II recurred.
  • Patients who were post-op 4-week ctDNA-negative patients did not derive significant benefit from ACT, with an HR of 1.3 in high-risk stage II and III.


  • This study shows that stratifying postsurgical treatment decisions using the assay can identify patients likely to benefit from ACT across all stages.
  • ctDNA dynamics from post-op 4-week ctDNA-positive to 12 weeks could become a new surrogate end point beyond DFS.
  • ctDNA-guided adjuvant strategy will further be established by ongoing randomized VEGA and ALTAIR studies and will be presented at future conferences.