Aspirin Did Not Prevent Colorectal Cancer Return After Liver Metastasis Treatment

Daily low-dose aspirin did not lower the risk of cancer coming back after treatment for colorectal cancer that had spread to the liver, according to final results of the phase 3 ASAC trial published online Sept. 23, 2026, in The Lancet Gastroenterology & Hepatology. Serious side effects were more common with aspirin than with a placebo (an inactive pill), and the researchers concluded the results do not support routinely starting aspirin for this purpose.

What the Trial Tested

Colorectal cancer most often spreads to the liver. When those liver tumors (called liver metastases) can be removed with surgery or destroyed with ablation, a procedure that uses heat or other energy to kill tumor cells, some patients can be treated with the goal of cure. Even so, the cancer often comes back.

Aspirin has drawn interest as an inexpensive way to lower that risk. Earlier observational studies, which look back at what happened to patients rather than assigning treatments, suggested people who took aspirin might do better, and an earlier trial called ALASCCA found that aspirin reduced recurrence in some people with colorectal cancer that had not spread and whose tumors had certain genetic changes.

ASAC was designed to test the question directly in people with liver metastases. The trial was randomized, meaning patients were assigned by chance, and double-blind, meaning neither patients nor their doctors knew who was getting aspirin. It enrolled patients at 14 hospitals in Norway, Sweden and Denmark who had finished curative-intent treatment for colorectal cancer liver metastases and were not already taking aspirin. Of 466 patients randomized, 428 started study treatment and were included in the main analysis. They took either 160 mg of aspirin once a day or a placebo.

The main goal was disease-free survival, the length of time patients lived without the cancer returning.

What It Found

Aspirin did not improve disease-free survival. The median time before the cancer returned or the patient died was 1.13 years with aspirin and 1.40 years with placebo, a difference that was not statistically significant. The researchers found no sign that aspirin worked better in patients whose tumors carried PIK3CA or KRAS gene changes.

Three years after starting treatment, 75.7% of patients in the aspirin group were alive compared with 84.9% in the placebo group. That difference was statistically significant, but the authors urged caution. Overall survival was a secondary goal, the trial was not designed mainly to measure it, and the researchers did not collect information on the treatments patients received after their cancer came back. Those later treatments could have affected survival.

"Our findings demonstrate why such treatments must be tested in rigorous randomised trials," Dr. Sheraz Yaqub of Oslo University Hospital and the University of Oslo, who led the trial, said in a news release.

Side Effects

Serious adverse events occurred in 17 of 217 patients (7.8%) who took aspirin and 4 of 211 patients (1.9%) who took placebo. No deaths were judged to be caused by the study treatment.

"We found no clear benefit in this group, while serious adverse events were more common," Dr. Ernesto Sparrelid said in a news release from Karolinska Institutet in Sweden.

What's Still Unknown

The trial does not explain why survival appeared lower in the aspirin group, and the researchers have said that finding should be interpreted carefully. They plan further molecular analyses to see whether tumor biology plays a role.

The results also apply to a specific situation: starting aspirin after curative-intent treatment of liver metastases in people who were not already taking it. The trial did not test whether people who already take aspirin should stop, and it does not change the findings from earlier trials in colorectal cancer that has not spread. The investigators noted that any benefit of aspirin may depend on the stage and biology of the cancer.

What It Means for You

If you have had surgery or ablation for colorectal cancer that spread to the liver, this trial does not support starting aspirin to keep the cancer from coming back. "There is no rationale for routinely initiating aspirin in these patients solely to prevent cancer recurrence," said Dr. Per Sandström of Linköping University Hospital, the trial's lead investigator in Sweden.

If you already take aspirin for another reason, such as heart health, do not stop on your own. Dr. Yaqub said the findings should not prompt patients taking aspirin for another condition to stop, and that any change should be discussed with a doctor.

Questions to Ask Your Care Team

• Is there any reason for me to take aspirin after my liver metastasis treatment?
• I already take aspirin for my heart. Should anything change?
• What follow-up scans and blood tests will help catch a recurrence early?
• Are there clinical trials testing ways to prevent recurrence that I could join?

References

1. "Aspirin After Curative-Intent Treatment of Colorectal Cancer Liver Metastases (ASAC): A Multicentre, Phase 3, Randomised, Double-Blind, Placebo-Controlled Trial." Yaqub S, et al. The Lancet Gastroenterology & Hepatology. Sept. 23, 2026.
2. "Large Scandinavian Trial Finds No Benefit of Aspirin After Treatment of Colorectal Cancer Liver Metastases." University of Oslo, Faculty of Medicine. Oct. 2, 2026.
3. "Aspirin Did Not Prevent Recurrence After Liver Metastasis Surgery." Karolinska Institutet. Sept. 29, 2026.

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