Pancreatic Cancer

Why Some People Survive Pancreatic Cancer Far Longer

The evidence here is strong for a survival finding, and it was replicated across two hospitals before anyone published it. Pancreatic cancer has among the worst outcomes of any common cancer, with fewer than one in ten people alive five years after diagnosis. Even among those whose tumours can be removed surgically, most die within five years. A small group doesn't, and working out why has produced one of the more surprising results in cancer research.

Tumours have their own bacteria

The first thing to establish is that this is possible at all.

Pancreatic tumours contain bacteria. Researchers confirmed it using several independent methods, including genetic sequencing and direct imaging of bacteria within tumour tissue.

That was unexpected. The pancreas is not a place bacteria were thought to live, and tumours were assumed sterile.

Where they come from appears to be the gut. The pancreatic duct opens into the small intestine, giving a direct route upstream.

The difference between long and short survivors

Researchers profiled the bacteria inside surgically removed pancreatic tumours, comparing people who survived more than five years against people who survived less.

They examined 68 tumours, 36 from long-term survivors and 32 from stage-matched short-term survivors, then repeated the analysis in a second cohort at a different hospital.

Long-term survivors had more varied bacteria inside their tumours.

Sorting patients by that measure alone produced a striking split. Those with high bacterial variety had a median survival of 9.66 years. Those with low variety had a median survival of 1.66 years.

That difference held independently of previous treatments, body weight and antibiotic use.

A specific combination of four organisms, including Bacillus clausii, predicted long survival in both cohorts.

Source: Tumor Microbiome Diversity and Composition Influence Pancreatic Cancer Outcomes

Testing whether the bacteria are doing the work

A survival difference could reflect something else about those patients. So the researchers moved the bacteria.

They transplanted stool from long-term survivors, from short-term survivors, and from healthy donors into mice carrying pancreatic tumours.

The transplants changed the bacteria inside the mouse tumours, which establishes that the gut community shapes the tumour community rather than the two being separate.

Tumour growth differed by donor group. So did the immune cells infiltrating those tumours.

That last point is the proposed mechanism. Tumours from long-term survivors contained more killer T cells, the immune cells that destroy cancer cells directly. A more varied tumour bacterial community appears to attract a stronger immune response.

The complication that stops this being simple

Other work points in what looks like the opposite direction, and both findings can be right.

A separate group found that removing bacteria with antibiotics slowed pancreatic tumour growth in mice, and that transplanting bacteria from tumour-bearing mice cancelled that benefit. In those experiments the bacteria were helping the tumour, apparently by suppressing immune responses.

The reconciliation is that variety and composition matter more than presence. Some bacterial communities inside tumours suppress immunity. Others provoke it.

That fits the human data, where it wasn't having bacteria that predicted survival but having a wide range of them.

It also explains why nobody is recommending antibiotics here. Wiping out the community removes the harmful and the helpful together.

Source: The Tumor Microbiome in Pancreatic Cancer: Bacteria and Beyond

What this means for you

Persistent upper abdominal or back pain, yellowing of the skin or eyes, or unexplained weight loss needs urgent medical assessment, and surgery followed by chemotherapy remains the only treatment offering long-term survival. In addition, the research above found people whose tumours contained a wide range of bacteria surviving a median of 9.66 years against 1.66 years for those whose tumours did not, with transplant experiments showing the gut community shaping what ends up inside the tumour. A varied, plant-rich diet supports the same gut bacteria this research ties to a more varied community and a stronger immune response. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.