Scientists in the US have uncovered a link between the number of different types of bacteria found in the tumours of people with pancreatic cancer and how long they live.
Using patient tumour samples, scientists at The University of Texas have shown that the more diverse the bacterial population in a pancreatic tumour, the better a patient’s prognosis.
The researchers, who published their work in Cell, also showed that transferring the bacteria from long-term survivors to mice with the disease could alter the types of bacteria found in the tumour.
The procedure, called a Faecal Microbiota Transplant (FMT), encouraged the mice’s immune systems to attack the disease.
Professor Phillip Quirke, a Cancer Research UK Grand Challenge medical scientist who studies bacteria and its relationship with cancer, called the study “fascinating”. Quirke said that this is the first sign that the bacteria in our bodies may help a patient’s immune system tackle their cancer.
The team studied samples from patients across two independent hospitals, one at MD Anderson in Texas and one at Johns Hopkins Hospital in Baltimore, to see if the types of bacteria found in a tumour had any impact on survival. Each group included both long and short-term survivors of pancreatic cancer.
The 22 long-term survivors from MD Anderson Hospital lived for 10 years on average. Whereas the short-term survivors lived an average of 1.6 years after diagnosis.
Clinicians at the Johns Hopkins Hospital had 15 patients that survived their cancer for 10 years or longer and 10 patients surviving less than 5 years.
By sequencing the genes of the different types of bacteria present in each tumour, they concluded that those with a high level of bacterial diversity in their tumours survived for 9.66 years on average, and those with low diversity 1.66 years.
They also showed that more immune cells flooded into tumours with more diverse bacteria, suggesting the bacteria can play an important role in helping the immune system fight cancer.
These patterns occurred regardless of other factors, such as previous therapies taken by the patients and antibiotic use.
Quirke said this study suggests that the bacterial content of a person’s pancreatic cancer may be a better predictor of how long they will live than the genetic faults fuelling the disease.
The team also identified three specific species of bacteria that could be associated with long-term pancreatic cancer survival. But Quirke said that further work is needed in a larger and more diverse group of patients before their importance can fully be confirmed.
More work needed to find new treatment options
Pancreatic cancer is a particularly hard-to-treat disease and survival is devastatingly low. The study authors say these new findings open up interesting avenues to explore in the hunt for future pancreatic cancer treatments.
“Results of the FMT experiments represent a significant therapeutic opportunity to improve pancreatic cancer treatment by altering the tumour immune microenvironment,” said senior author Florencia McAllister, assistant professor of Clinical Cancer Prevention at MD Anderson. “There is promise here but we have a lot of work ahead.”
Whilst underlining that a lot more work is needed, McAllister said the results of the experiments in mice “represent a significant therapeutic opportunity to improve pancreatic cancer treatment by altering the tumour immune microenvironment.”
Quirke added that “progress has been very slow in pancreatic cancer research so any increase in our understanding of the disease is very positive.
“Next, the researchers need to confirm the link between bacterial diversity and survival in larger groups of patients, as well as patients who live in other countries. It would also be interesting to see if this link could be shown to have the same effects on other tumour types,” he added.
Riquelme, E et al. (2019) Tumor Microbiome Diversity and Composition Influence Pancreatic Cancer Outcomes. Cell DOI: https://doi.org/10.1016/j.cell.2019.07.008