Stool samples from 1,364 cancer patients revealed different patterns of the gut microbiome in five cancer groups. Mayo Clinic scientists also compared the data with samples from 287 people without cancer, taking the materials before the start of a new treatment.
The study is published in the scientific journal Cell. The patients were treated at Mayo Clinic sites in Minnesota, Arizona and Florida and had a variety of types and stages of disease.
Differences in younger patients
After accounting for the influence of other diseases and clinical factors, the researchers identified 341 bacterial species associated with five groups of cancers. The clearest age differences were found in colorectal cancer and breast cancer.
In patients 50 years of age or younger with colorectal cancer, higher levels of lactate and a greater abundance of the bacterium Veillonella parvula were measured. It uses lactate for growth, and tumors themselves can produce high amounts of this substance. However, the link does not prove that the bacteria cause the early onset of the disease.
Younger breast cancer patients reported changes in 64 bacterial species and lower levels of primary bile acids. Among the different microorganisms was Clostridium scindens, which is involved in the metabolism of bile acids and steroids. In the analysis of brain cancer patients, similar age-related changes were not found.
Link to survival and chemotherapy
Scientists also found bacterial profiles associated with survival in colorectal cancer, liver and internal bile duct cancer, melanoma, ovarian cancer and prostate cancer. In liver and internal bile duct cancer, Bifidobacterium longum was associated with longer survival, while Blautia massiliensis was associated with shorter survival.
A separate part of the study looked at the side effects of chemotherapy. Among patients who received 5-fluorouracil, those who later developed diarrhea had fewer bacterial genes capable of breaking down the drug. Much of this function was attributed to Anaerostipes hadrus. The same association was not seen in patients treated with carboplatin, suggesting that the signal may be specific to 5-fluorouracil.
“The microbiome is not the only factor in cancer or treatment outcomes, but it is a component that has been under-recognized,“ says Purna Kashyap of the Mayo Clinic.Reuben Mars, one of the study's authors, said the findings allow the search to be directed at microbial changes specific to individual cancers. He said this is necessary to test whether the microbiome has a causal role and whether targeted interventions can be developed.
The results so far show associations, not cause and effect. The researchers plan to test the signals in larger and more diverse groups of patients and assess whether microbiome analysis can help predict side effects of treatment.
Source: newsweek.com