Microbes Found in the Lungs Are Linked with Worse Lung Cancer Outcomes
Once thought sterile, lungs can harbor microbes that may affect lung cancer pathogenesis and prognosis.
If microbes normally found in the mouth get into the lungs as well, their presence in patients with lung cancer was associated with a more advanced stage of disease and worse prognosis, according to a study just published in Cancer Discovery, a journal of the American Association for Cancer Research (AACR).
“The lungs were long thought to be sterile, but we now know that oral commensals—microbes normally found in the mouth—frequently enter the lungs due to unconscious aspirations,” said Leopoldo Segal, MD, director of the Lung Microbiome Program and assistant professor of medicine at the New York University Grossman School of Medicine.
Segal and colleagues analyzed the lung microbiome – the population of microbes living in the lungs – of 83 untreated adult patients with lung cancer using samples obtained from bronchoscopies performed to help diagnose the disease. Samples were analyzed to identify the specific microbes, which included Streptococcus and several other types of bacteria.
The researchers found that patients who had advanced stage lung cancer (stages IIIB-IV) had greater amounts of oral microbes living in the lungs than those who had early-stage disease (stages I-IIIA). Furthermore, the presence of these microbes was associated with decreased survival of the patients, even after the data were adjusted for the stage of the tumor.
Poor prognosis was associated with greater levels of Veillonella, Prevotella, and Streptococcus bacteria in the lung microbiome, and tumor progression was associated with Veillonella, Prevotella, Streptococcus, and Rothia bacteria.
Previous research by Segal has shown that the presence of microbes in the lung can activate the immune response, in which proteins cause an inflammation that can influence the progression of lung cancer and its prognosis. The inflammatory proteins included the cytokine IL-17. Segal and colleagues conducted experiments with laboratory mice which showed that using an antibody to IL-17 resulted in a reduction in tumor burden.
“Given the results of our study, it is possible that changes to the lung microbiome could be used as a biomarker to predict prognosis or to stratify patients for treatment,” said Segal. “Another exciting possibility is to target the microbiome itself or the host response to microbes as a form of cancer therapy. Our results using an antibody against IL-17 suggest that this could be an effective strategy.”