Colon and rectal cancer is one of the most common and deadliest cancers in Sweden. Close to 7,000 people are affected each year. Now an extensive Nordic clinical trial, the Alaska study, shows that one of the world's cheapest and most proven drugs – acetylsalicylic acid, the active substance in Magnecyl, Treo, Aspirin and Trombyl, among others – can halve the risk of recurrence in a large patient group after surgery.
The study has been led by Anna Martling, professor of surgery at the Karolinska Institute and chief physician at the Karolinska University Hospital. She has been researching colorectal cancer since the late 1990s and describes the results as an unusually large breakthrough.
- I will never forget the moment when our statistician presented the numbers and curves. It gave an almost unreal feeling. Being able to show a halved recurrence risk, and at the same time increase survival by ten percentage points in absolute terms, is a result you hardly dare to dream of as a researcher, says Anna Martling.
The breakthrough lies in the fact that the treatment could be individually adapted. The clear risk reduction applies to patients whose tumors carry a mutation in the so-called PI3K signaling pathway, a change found in around 40 percent of all people with bowel cancer. When the signaling pathway is mutated, cells become overactive and divide uncontrollably. Acetylsalicylic acid blocks the enzyme that drives the process. The drug also prevents platelets from hiding circulating tumor cells, which can make them more visible to the body's immune system.
The findings raise the question of whether more people should be taking Aspirin or Treo for prevention. However, the researchers clearly warn against self-medication without a doctor's prescription. As the substance inhibits blood coagulation and can damage the stomach lining, daily use increases the risk of serious bleeding and stomach ulcers.
- I do not take acetylsalicylic acid daily for that very reason. However, I now rather choose a Treo than paracetamol for occasional headaches, says Anna Martling.
For patients with the right gene profile, the benefits clearly outweigh the risks. In the study, which included 3,500 patients at 33 Nordic hospitals, only four people in the treatment group suffered side effects that could be linked to the drug.
The results have already had an impact in healthcare. In February 2026, the national care program for colon and rectal cancer was updated with a new recommendation. It's an unusually quick change – guidelines are normally updated every three years – but the results were deemed too important to wait. Gene sequencing of the tumor is now recommended in conjunction with surgery, so that patients with the relevant mutation can be offered three years of treatment with low-dose acetylsalicylic acid.
- It marks an important step for Swedish precision medicine, where a simple standard preparation gets a new role in the treatment of cancer, says Anna Martling.
