Karolinska Institutet

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The Link Between Gut Bacteria and Cancer Treatment

Lars Engstrand is a physician and professor at Karolinska Institutet in Stockholm, and the director of Centre for Translational Microbiome Research (CTMR). For more than 30 years, he has been studying the microorganisms in the gastrointestinal tract, and he was one of the first to study the intestinal flora with new and powerful DNA techniques. In his spare time, Lars enjoys singing and is a member of the male choir Orphei Drängar.

Why do people with cancer respond differently to cancer treatment? In recent years, outcomes for cancer patients have improved thanks to so called immunotherapy, a type of treatment that engages the immune system to attack tumors. Immunotherapy has proven to be effective, and some say it is set to revolutionize the treatment of cancer. However, some patients respond better than others, and in around two-thirds of people, cancers are resistant to this type of treatment. For a while now, researchers have been trying to figure out why. Immunotherapies unleash the body’s immune system to fight cancer cells – why patients respond differently to this treatment remains a mystery.

New research is showing a link between a person’s gut microbiome and the effectiveness of cancer immunotherapy. It seems like the bacteria found in a patient’s digestive tract can in fact affect the outcome of the treatment. Understanding which patients will benefit from immunotherapy is a big challenge, and this research is a step towards identifying these people. Certain bacteria seem to boost the effectiveness of the treatment and, if we alter the composition of the microbiome, we may be able to influence the outcome of the treatment and help the body’s immune system fight the disease.

Clinical studies of how to improve responses to immunotherapy are underway. In some studies, cancer patients are given supplements of cultivated bacteria from people who have previously responded well to immunotherapy. In others, researchers are exploring the possibility of altering patients’ gut bacteria through microbiota transplants from people with strong responses to these therapies. All in the hopes of helping the immune system to recognize and better attack the cancer cells.

These are very early-stage studies. How some bacteria are able to trigger our immune system to fight the cancer is still unknown, and researchers from both America and Europe are looking for answers. Changing your eating habits is another way to affect the microbiome, and thereby influence the effectiveness of immunotherapy. But more research has to be done. However, a widely accepted hypothesis is that a good gut microbiome can join the fight against cancer.

Our group of scientists is exploring the gut microbiome in the healthy population, in hopes of understanding what makes up a healthy microbiome and how it affects the human body. In the future, this will help us evaluate the role of probiotic supplements in the treatment or prevention of various diseases.

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