Gut bacteria mark the efficacy of chemotherapy in breast cancer

A group of researchers studying the activity of intestinal bacteria has found a possible link between them and the effectiveness of chemotherapy

The study, presented at the 12th European Congress on Breast Cancer, includes a small group of women who were being treated with chemotherapy before undergoing surgery. In some of them, in which chemotherapy appeared to kill all cancer cells, the researchers observed a particular pattern in the activity of gut bacteria before and after treatment.

Ultimately, the researchers say, understanding the relationship between the two phenomena could help researchers make chemotherapy more effective for more cancer patients.

The research has been presented by Kirsty Ross, Beatson West of Scotland Cancer Center (Glasgow, UK). “Oftentimes, patients with breast cancer receive chemotherapy before surgery. Tests carried out on the tissues that are removed during surgery can then show how sensitive the cancer is to chemotherapy. If all the cancer cells have been killed, that predicts a very high chance of a cure for the patient. However, in many patients, we find cancer cells in the removed tissue, and these people are at higher risk of relapse.

“There are probably many different reasons why chemotherapy works better for some patients than others. In this study, we have begun to look at whether the function of the gut microbiome may be a factor influencing the efficacy of chemotherapy.

Ross and his colleagues on the research team analyzed the patients’ gut bacteria by measuring the amount of short-chain fatty acids (SCFAs) in their stool samples. These compounds are produced by bacteria in the gut when they break down the fiber in food.

There are many different reasons why chemotherapy works better for some patients than others.

The study included two groups of women, of similar weight and age: one made up of 21 patients with early-stage breast cancer and the other of 21 healthy women. All cancer patients were treated with chemotherapy at the Beatson West of Scotland Cancer Center and then underwent surgery. The tissue removed during the operation was analyzed to see if cancer cells remained in it.

The healthy women, the researchers took samples and performed a series of SCFA tests. In women with cancer, samples were taken before chemotherapy began, and also in the middle of treatment and after it ended. And they found similar levels of SCFA in healthy and sick women at the beginning of treatment.

However, when they took a closer look at SCFA levels in cancer patients, they found there were differences between those whose chemotherapy had been effective against cancer and those who still had cancer cells in their breasts.

SCFAs exert an influence on the immune system, by promoting the development of a type of cell called regulatory or suppressor T lymphocytes.

Specifically, they found low concentrations of two SCFAs (propionate and butyrate) in samples taken before and after treatment in women who responded well to chemotherapy, compared to those in patients who did not respond as well.

Previous studies had already shown that these SCFAs exert an influence on the immune system, by promoting the development of a type of cells called “regulatory or suppressor T lymphocytes”, which are known to reduce the ability of the immune system to fight cancer cells.

‘We cannot say for sure that the various levels of SCFA are the cause of the different responses to chemotherapy and we need to investigate this question further. But it seems possible because we already know that these compounds play a role in the immune system. It could be that the organisms of patients with lower levels of a particular SCFA are better able to activate an immune response in conjunction with chemotherapy, and we will verify this in future studies, “said Dr. Ross.

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