• Taking antibiotics within a few months of starting immune checkpoint inhibitor (ICI) therapy can make the treatment less effective in treating non-small cell lung cancer (NSCLC), a new study found.
• In a meta-analysis of more than 12,000 participants, researchers found that taking antibiotics with ICI significantly reduced overall survival and progression-free survival.
• Researchers believe that antibiotics may harm gut bacteria that make ICI therapy effective.

People with NSCLC who take antibiotics within a couple of months of starting ICI therapy are almost twice as likely to see their cancer progress, compared to those who don’t take antibiotics, according to a recent study. They also have a lower chance of responding to ICI treatment — a type of immunotherapy — in general.

Immune checkpoint inhibitors are a type of immunotherapy used to treat lung cancer. ICI drugs allow the body’s immune system to kill cancer cells.

The results were presented by a group from Paris at the Society of Immunotherapy of Cancer 2021 Annual Meeting as an expansion of their earlier 2020 study.

Gut Bacteria and Response to Cancer Therapies

Antibiotics are used to treat bacterial infections, but they can also harm the body’s naturally occurring bacteria. Bacteria in the intestines — known as the gut microbiome — are affected by antibiotics. In fact, antibiotics can kill off diverse bacteria, affect metabolism, and disrupt the overall balance of the gut.

Previous studies have found that bacteria in the intestines may influence how well people respond to ICI treatment — particularly in cases of non-small cell lung cancer. Other studies have found that the gut microbiome can affect response and even resistance to other cancer-fighting drugs like chemotherapy.

In order to understand the extent of the impact that antibiotics have on ICI response, researchers from the French biotechnology company Da Volterra performed a meta-analysis on 35 studies of people with NSCLC who were treated with antibiotics and ICIs.

Antibiotics Make ICI Therapies Less Effective

The researchers compiled data from major oncology conferences and PubMed that discussed people with NSCLC who were treated with antibiotics and ICI. In all, 35 studies with a total of 12,235 participants were included in the study.

The studies used overall survival and progression-free survival as the end points — both are used to see how well different treatments work. Overall survival refers to the length of time a person lives from the time they are diagnosed or start to receive treatment. Progression-free survival refers to the time during and after cancer treatment that a person’s cancer doesn’t worsen.

Overall, people who received antibiotics within two months before or after beginning their ICI treatment had significantly worse overall survival and progression-free survival compared to those who did not receive any antibiotics or those who received them outside of two months.

Those who took antibiotics around the same time as starting ICI therapy also had a 44 percent decrease in their overall response rate to treatment, while the chances of their cancer progressing almost doubled.

The researchers believe these effects may be due to antibiotics eliminating helpful gut bacteria that can boost the body’s immune system against cancer.