Adjuvant Aspirin Fails to Prevent Liver Metastasis Recurrence in Colorectal Cancer

A major Scandinavian clinical trial has concluded that taking daily low-dose aspirin after surgery for colorectal cancer liver metastases does not prevent the disease from returning. The phase 3 ASAC trial found that the widely available medication offered no disease-free survival benefit.[1][3][4]

Instead of protecting patients, the intervention was associated with a higher rate of serious side effects and a lower overall survival rate at three years. The findings definitively close the door on using aspirin as a routine adjuvant therapy for this specific patient population.[1][4]

"Our results show that aspirin should not be routinely recommended to prevent recurrence after curative-intent treatment of colorectal cancer liver metastases," said Sheraz Yaqub. Yaqub serves as a professor at the University of Oslo and a consultant hepatobiliary surgeon at Oslo University Hospital.[1]

The results highlight a critical biological distinction in how tumors respond to treatment at different stages of progression. While aspirin has shown promise in preventing early-stage colorectal cancer, those anticancer effects clearly do not extend to metastatic disease in the liver.[1][4]

A Stubborn Clinical Challenge

Colorectal cancer remains one of the most common malignancies worldwide, and its tendency to spread makes it particularly lethal. Up to 50 percent of patients with the disease will develop liver metastases during the course of their illness.[1][2][3]

Once the cancer reaches the liver, the clinical picture becomes significantly more complex. "Patients rarely die from the primary tumour itself. It is the metastatic disease that is usually life-threatening," Yaqub explained.[1]

For patients with liver metastases, surgical resection or local ablative therapies offer the only realistic chance of a long-term cure. Surgeons physically remove the visible tumors from the liver, aiming to leave the patient entirely disease-free.[1][2]

However, the procedure is rarely the end of the story. Even after successful curative-intent surgery, the cancer returns in more than half of all patients. This reality drives an urgent search for effective adjuvant therapies that can keep the disease at bay.[1][2]

The Rationale for Aspirin

Aspirin has attracted considerable attention in oncology research for more than a decade. The inexpensive, widely available painkiller and anti-inflammatory drug has well-documented effects on cellular pathways that are frequently hijacked by developing tumors.[1][5]

Previous observational studies suggested that long-term aspirin use was associated with a reduced risk of developing primary colorectal cancer. Those population-level findings spurred researchers to investigate whether the drug could also act as a secondary preventive measure after a cancer diagnosis.[1][5]

Recent randomized trials provided encouraging evidence for that hypothesis in early-stage disease. The ALASCCA trial, for example, demonstrated that adjuvant aspirin reduced recurrence in selected patients with non-metastatic colorectal cancer whose tumors carried specific PI3K pathway alterations.[1][2]

Those successes prompted the design of the ASAC trial, which aimed to test whether the same inexpensive intervention could protect patients with advanced disease. Researchers hoped that a daily pill could offer a simple, accessible defense against liver metastasis recurrence.[1][5]

The ASAC Trial Design

To answer the question definitively, investigators launched a randomized, double-blind, placebo-controlled phase 3 trial across 14 hospitals in Norway, Sweden, and Denmark. The Scandinavian collaboration enrolled 466 patients between 2017 and 2022 who had recently undergone curative-intent treatment for colorectal cancer liver metastases.[1][4]

The trial specifically excluded patients who were already taking aspirin or other blood thinners for cardiovascular conditions. Of the initial cohort, 428 patients officially initiated the study treatment and were included in the primary efficacy analysis.[4][5]

Participants were randomly assigned to receive either 160 milligrams of aspirin once daily or a matching placebo. The treatment was scheduled to continue for up to three years, or until the patient experienced a cancer recurrence, unacceptable toxicity, or death.[4][5]

The primary endpoint of the study was disease-free survival, measuring the time from the start of treatment until the cancer returned or the patient died from any cause. Secondary endpoints included overall survival, time to recurrence, and detailed safety metrics.[4][5]

Efficacy and Safety Results

The final analysis, published in The Lancet Gastroenterology & Hepatology on September 23, 2026, revealed that the intervention failed its primary objective. Aspirin did not improve disease-free survival compared with the placebo control group.[4][5]

The median time before the cancer returned or the patient died was actually shorter in the treatment arm. Patients taking aspirin experienced a median disease-free survival of 1.13 years, compared with 1.40 years for those taking the placebo.[4]

Furthermore, the researchers found no evidence that the drug worked better in specific molecular subgroups. Patients whose tumors carried PIK3CA or KRAS mutations derived no additional survival benefit from the daily aspirin regimen, contradicting earlier hopes.[1][4]

The safety profile of the intervention also heavily favored the placebo. Serious adverse events occurred in 7.8 percent of patients in the aspirin group, compared with just 1.9 percent of the patients in the control group.[2][4]

The severe side effects observed in the aspirin cohort included gastrointestinal bleeding, duodenal ulcers, epistaxis, and cerebral hemorrhage. While no treatment-related deaths occurred, the elevated risk of bleeding complications was clinically significant for a post-surgical population.[2][4]

Overall Survival Caveats

The trial data also showed a concerning trend in overall survival. At the 36-month mark, 76 percent of the patients receiving aspirin were still alive, compared with 85 percent of the patients in the placebo group.[4]

However, the investigators urged caution when interpreting that specific survival metric. Overall survival was a secondary endpoint, meaning the trial was not statistically powered to definitively measure differences in long-term mortality between the two groups.[4]

Additionally, the researchers did not collect comprehensive data on the subsequent therapies patients received after their cancer returned. Variations in those later-line treatments could have influenced the final survival numbers independently of the initial aspirin intervention.[4]

Despite those caveats, the combination of no efficacy, higher toxicity, and potentially worse survival paints a clear clinical picture. "With no demonstrated benefit and a higher rate of serious adverse events, there is no rationale for routinely initiating aspirin in these patients," said Per Sandström of Linköping University Hospital.[2]

Clinical Implications

The ASAC trial results underscore the danger of extrapolating treatment benefits from early-stage cancer to metastatic disease. Tumor biology changes fundamentally as cancer spreads through the body, significantly altering how malignant cells respond to systemic therapies.[1][2]

"What works for one group of patients does not necessarily work for another," Yaqub noted. "We cannot simply transfer results from patients with primary colorectal cancer to patients who have been treated for liver metastases."[1]

The findings will help refine international oncology guidelines, ensuring that adjuvant aspirin is reserved strictly for the non-metastatic populations where it has proven effective. Preventing unnecessary prescriptions will spare advanced-stage patients from avoidable and severe bleeding risks.[2][5]

Guidance for Current Patients

The researchers emphasized a crucial distinction for patients currently managing their health and medications. The trial only evaluated the effects of initiating aspirin specifically as a new anticancer treatment immediately following curative liver surgery.[1][2]

The results do not apply to patients who are already taking daily aspirin for established cardiovascular indications, such as a previous heart attack or stroke. The cardiovascular benefits of the drug in those populations remain well-documented and life-saving.[1][2]

"Patients who are already taking aspirin for cardiovascular disease or other medical indications should not stop treatment because of these findings," Yaqub advised. "Any changes should always be discussed directly with their treating physician."[1]

Moving forward, the research team plans to utilize the trial's extensive biobank to further investigate the molecular characteristics of colorectal cancer liver metastases. They hope to identify new, more effective targets for adjuvant therapy that can genuinely prevent recurrence.[1][5]