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ASCO 2026 | ctDNA dynamics & adjuvant chemotherapy benefit CRC in the GALAXY trial
Mitsuru Yokota, MD, PhD, Kurashiki Central Hospital, Kurashiki, Japan, discusses findings from the GALAXY study (UMIN00039205) evaluating circulating tumor DNA (ctDNA) dynamics to guide adjuvant chemotherapy in resected stage I to IV colorectal cancer (CRC). The analysis demonstrated that patients who were initially circulating tumor DNA-negative at four weeks post-surgery but converted to positive at twelve weeks derived significant disease-free survival benefit from adjuvant chemotherapy. Conversely, patients remaining negative at both timepoints had favorable outcomes regardless of treatment. This interview took place during the 2026 American Society of Clinical Oncology (ASCO) Meeting in Chicago, IL.
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Transcript
This study is part of the Circulate Japan Galaxy study, and it evaluated whether serial ctDNA testing after surgery can help identify colorectal cancer patients who may still benefit from chemotherapy. In colorectal cancer, adjuvant chemotherapy is usually selected based on pathological stage and pathological clinical risk factors. However, these factors do not directly measure molecular residual disease...
This study is part of the Circulate Japan Galaxy study, and it evaluated whether serial ctDNA testing after surgery can help identify colorectal cancer patients who may still benefit from chemotherapy. In colorectal cancer, adjuvant chemotherapy is usually selected based on pathological stage and pathological clinical risk factors. However, these factors do not directly measure molecular residual disease. ctDNA is a blood-based marker that can detect residual disease after surgery and provide important prognostic information. In this analysis, we focused on patients who were ctDNA negative at the first post-operative time point, approximately four weeks after surgery, and then had a second ctDNA test at approximately 12 weeks after surgery. Among 1950 eligible patients, 97% remained ctDNA negative at both time points. These patients had favorable outcomes regardless of adjuvant chemotherapy. Their two-year disease-free survival was 84.7% with observation and 86.1% with adjuvant chemotherapy. This suggests the additional benefit from chemotherapy is limited in patients with sustained ctDNA negativity. In contrast, 56 patients (3%) converted from ctDNA negative at 4 weeks to ctDNA positive at 12 weeks. We consider this pattern to represent early molecular recurrence. In this subgroup, patients who received adjuvant chemotherapy appeared to have better disease-free survival than those who were observed without chemotherapy. The two-year disease-free survival improved from 10% to 38.5% and median disease-free survival improved from 2.2 months to 12.9 months. The important limitation is that this was a prospective observational analysis, not a randomized trial. Chemotherapy was not assigned by the protocol, and the number of patients who converted to ctDNA positive was small. Therefore, these findings should be considered exploratory and hypothesis-generating. The key message is that a single negative ctDNA test after surgery may be insufficient for some patients. Serial ctDNA testing at 4 and 12 weeks may help identify initially ctDNA negative patients who develop early molecular recurrence and could still benefit from chemotherapy before radiological recurrence.
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