A role for the pulmonary microbiome?

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A recent review examines the role of the lung microbiome in lung cancer. Tatiana Maksimova/Getty Images
  • Scientists looked at the evidence that links the community of microorganisms living in the lungs – the lung microbiome – to lung cancer.
  • They conclude that there are opportunities to use the microbiome to diagnose lung cancer at an early stage and improve the chances of survival for people with the disease.
  • However, many uncertainties remain about how certain bacteria contribute to lung cancer.
  • Unlike the gut microbiome, the lung microbiome is difficult to sample and study.

Experts believed that healthy lung tissue is a sterile, germ-free environment. However, recent advances in genome sequencing technology have shown that this is not the case.

The latest research suggests that the community of bacteria, fungi, and viruses that live in the lungs, known as the lung microbiome, has links to several respiratory conditions.

These conditions include chronic obstructive pulmonary disease (COPD), asthma, and cystic fibrosis.

Additionally, microbiomes in the gut, mouth, and lungs can interact to cause lung disease.

Researchers led by Shanghai Jiao Tong University School of Medicine in China examined existing knowledge about the links between microbiomes and lung cancer and how this could aid in the diagnosis and treatment of the disease in the lung. ‘to come up.

They report their findings in the newspaper npj Precision Oncology.

Lung cancer is the leading cause of cancer-related death worldwide. This is mainly because individuals show few symptoms in the early stages, which means around 75% of cases are advanced when doctors diagnose them.

Treatment options for advanced lung cancer are limited and the prognosis is poor.

In the United States only, approx. 130,000 people are likely to die from the disease in 2022.

“Therefore, early detection and improved treatments for lung cancer are becoming increasingly urgent,” the review authors state.

They report that in healthy lungs, Propionibacterium, Streptococcus, Haemophilusand Veillonelle bacteria coexist with fungi such as Aspergillus, Penicilliumand candidiasis.

On the other hand, Pseudomonas, Streptococcus, Staphylococcus, Veillonellaand Moraxella bacteria are often associated with lung cancer.

“However, there is no widely accepted consensus definition of healthy or harmful lung microbiota,” the researchers said.

A Pilot study 2019 found associations between lung microbiota and participants’ chances of survival.

“We took our research further in a large study, showing the lung microbiome as a potential predictive biomarker of lung cancer treatment outcomes,” said lead author Prof. Jiyoung Ahn, Ph.D., Molecular Epidemiologist of the cancer at New York University School. of Medicine.

She said Medical News Today that the document is currently undergoing peer review prior to publication.

“I think the microbiome is a potential biomarker of cancer treatment outcomes, which helps patients and clinicians make informed decisions, but we still need rigorous studies to test the hypothesis,” said the professor. Ahn.

The communities of microbes that live in the lungs, mouth and gut seem to interact.

According to the researchers, this can happen directly through the dispersal of mucus and through respiratory and digestive processes, or it can happen indirectly via immune factors and metabolic products in the blood.

Research suggests these modes of communication may allow “unfriendly” gut microbes to play a role in lung conditions, such as COPD, asthma, cystic fibrosis and lung cancer.

Additionally, a 2018 study found that people with lung cancer had more oral bacteria in their lungs than participants in the control group. The study authors link the presence of the bacteria to increased activity in cancer signaling pathways.

How these interactions work remains elusive.

The authors of this review conclude,

“Understanding the relationship between the human microbiota, especially the gut microbiota, and lung cancer, may open a new window for the diagnosis and treatment of lung cancer.”

However, possible treatments, which include probiotics, special diets and transplants of fecal microbiota from healthy individuals, remain at a very early stage of development.

Additionally, the authors note that taking samples directly from the lungs involves technical and ethical challenges. This is not the case for the intestinal microbiota, which is relatively easy to study from fecal samples.

The researchers write that, therefore, most studies of the lung microbiota rely on nasal secretions, saliva, sputum, and a diagnostic test that involves passing fluid through a small portion of the lung. Experts call this bronchoalveolar lavage.

The authors suggest several ways bacteria could cause lung cancer.

For example, damage to the lining of the lungs that is not repaired quickly could upset the balance of microbes and cause inflammation, possibly leading to cancer over time.

Older research in mice suggests that bacteria in the lungs could trigger inflammation, which in turn can lead to the development of lung cancer.

Alternatively, toxins or metabolites produced by bacteria could directly damage human DNA.

On the positive side, the researchers write that there is “invaluable” potential to improve different treatments for lung cancer, including radiation therapy, chemotherapy, surgery and immunotherapy.

For example, probiotics or faecal microbiota transfers could optimize gut microbiota to improve chemotherapy efficacy and minimize side effects.

There are also clues that the gut microbiome helps determine the success of immune therapy.

In a 2019 study, participants with a greater diversity of bacterial species in their gut microbiota responded better to immunotherapy for an advanced type of lung cancer.

In contrast, a 2017 study found that antibiotics significantly reduced the effectiveness of immunotherapy.

The review authors point out, however, that many more studies and clinical trials will be needed to determine whether modulating the gut microbiota can improve responses to lung cancer treatment.