Researchers have identified specific gut bacteria that correlate with cardiovascular biomarkers indicating increased risk of heart damage during chemotherapy in patients with breast cancer, according to new findings from the CARDIOCARE study, presented at the European Society of Cardiology's European Cardio-Oncology 2025 congress.

The prospective clinical study examined 98 women over age 60 diagnosed with breast cancer from three European cancer treatment centers and found that patients with higher relative abundance of Bacteroidaceae family bacteria showed statistically significant increases in cardiac biomarkers associated with treatment-induced cardiotoxicity.

Key Findings

The research demonstrated positive correlations between Bacteroidaceae relative abundance and multiple cardiac risk indicators:

• Left ventricular global longitudinal strain (LV-GLS): rs = 0.39, P < 0.0003

• Troponin I: rs = 0.21, P < 0.04

• N-terminal pro-B-type natriuretic peptide (NTproBNP) at the genus level: rs = 0.40, P < 0.00002; rs = 0.21, P < 0.04

All correlations were statistically significant (P < 0.05), based on Spearman’s rank correlation with confirmation via permutation testing.

“We saw a clear association between some specific genus of gut bacteria and cardiac biomarkers that suggest patients are at greater risk of heart damage during chemotherapy,” said Athos Antoniades, PhD, Head of Research and Development at Stremble Ventures LTD, who led the multi-omics analysis, including gut microbiome DNA sequencing.

Clinical Methodology

The study recruited participants from the Bank of Cyprus Oncology Centre (Cyprus), the National and Kapodistrian University of Athens (Greece), and the European Institute of Oncology (Italy). All women underwent comprehensive cardiac assessment, including echocardiograms to evaluate heart function and blood testing for cardiotoxicity biomarkers, prior to cancer treatment initiation.

Genetic sequencing profiled the complete bacterial composition of patients' gut microbiomes prior to chemotherapy. Researchers measured left ventricular ejection fraction (LVEF), LV-GLS, troponin I, and NTproBNP levels as primary cardiovascular endpoints. While all four markers were measured, only LV-GLS, troponin I, and NTproBNP showed statistically significant associations with gut microbiota composition.

Bacteroidaceae Characteristics

The study identified Bacteroides as the specific bacterial genus most prevalent in patients with elevated cardiotoxicity biomarker levels.

“The gut bacteria profile of these patients were similar to those found in patients with heart failure,” the researchers reported.

Bacteroidaceae represent a family of common gut bacteria that can confer health benefits but may cause harm when populations become dysregulated. These bacteria are implicated in inflammation and may trigger infections in extraintestinal tissues.

Research Context

“To allow cancer survivors healthier lives, we need to find new ways to protect them from the long-term side-effects of chemotherapy. This study is one of the first to ask whether the microbiome could play a role in how well patients’ hearts fare during chemotherapy,” explained Dr. Antoniades.

Cardiotoxicity is a relatively frequent adverse effect of many cancer therapies, including chemotherapy. As treatment success rates for breast cancer continue to improve, the long-term cardiac safety of survivors is an increasing clinical priority.

Future Research Directions

This study is part of the larger EU Horizon 2020-funded CARDIOCARE project (Grant agreement ID: 945175), which will expand to include 600 women to validate these early findings.

“We are already following up these 98 patients after chemotherapy, and are expanding the research project to all 600 patients already enrolled in the CARDIOCARE clinical trial,” Dr. Antoniades said.

“While further research is needed, it does give us the tantalising hope that tailored probiotics could play a role in protecting patients against the harmful effects of cancer treatment in future,” he added.

The research was presented at the European Cardio-Oncology 2025 scientific congress held in Florence, Italy, June 20–21, 2025.

Funding: This research was supported through the EU Horizon 2020 project CARDIOCARE (Grant agreement ID: 945175). All authors reported no conflicts of interest.