The human GUT microbiome and incident breast cancer: a prospective epidemiologic approach

The National Cancer Institute awarded Rutgers The State University of New Jersey, School of Nursing, $723,569 under the Cancer Cause and Prevention Research program (CFDA 93.393) on September 1, 2026, to conduct a prospective epidemiologic study examining associations between the human gut microbiome and postmenopausal breast cancer risk.

The research leverages the Nurses' Health Study II cohort, which includes over 18,000 women with pre-diagnostic stool samples and repeated assessments of diet and lifestyle. The study integrates stool metagenomics and metabolomics with circulating sex hormone and inflammation biomarkers to evaluate whether specific gut microbial features—including taxonomic composition, functional pathways, and stool microbial metabolites—contribute to breast cancer risk through hormone-related and non-hormonal mechanisms. The first aim identifies associations of pre-diagnostic microbial features in relation to subsequent breast cancer risk in a nested case-control study with 500 incident breast cancer cases and 500 matched controls, stratified by estrogen receptor status. The project addresses a critical gap in existing literature by providing the first large-scale prospective study applying whole-metagenome sequencing to characterize the stool microbiome and metabolome before breast cancer diagnosis, establishing whether microbiome alterations are causal or consequential to disease.

Work is performed in Newark, New Jersey. The project period runs through August 31, 2031. The award is classified as a Project Grant, an assistance type supporting investigator-initiated research.

Abstract

The etiology of postmenopausal breast cancer is complex, as reflected by the influence of hormonal and other non-hormonal factors across the life course. Emerging evidence suggests the GUT microbiota and microbial metabolites may contribute to risk by regulating estrogen metabolism, systemic immunity, and inflammation. However, existing human studies are all retrospective and have not applied the whole-metagenome sequencing approach to provide species-level resolution. No prospective epidemiologic studies have characterized the GUT microbiome before breast cancer diagnosis, nor systematically examined the stool microbiome and stool metabolome in breast cancer etiology using a multi-omics approach, leaving a critical GAP in understanding whether microbiome alterations are a cause or consequence of disease. Leveraging the nurses' health study II, which includes over 18,000 women with pre-diagnostic stool samples, repeated assessments of diet and lifestyle, and paired blood samples in a subset, we propose the first large-scale prospective study integrating stool metagenomics, stool metabolomics, and circulating SEX hormone and inflammation biomarkers to evaluate GUT microbiome contributions to breast cancer risk. Our central hypothesis is that specific GUT microbial features, including taxonomic composition, functional pathways, and stool microbial metabolites, are associated with breast cancer risk via hormone-related and non-hormonal mechanisms, and that these microbial features are shaped by host exposures across the life course. In aim 1, we will identify associations of pre-diagnostic microbial taxonomic, functional pathways, and metabolomic features in relation to subsequent breast cancer risk in a nested case-control study with 500 incident breast cancer cases and 500 controls, overall and by estrogen receptor status. In aim 2, we will examine associations between the fecal microbiome and plasma hormone and inflammation proteomics biomarker levels, and derive estrobolome-, testerobolome-, and inflammation-related microbial signatures, and elucidate how these signatures may be associated with breast cancer risk. In aim 3, we will evaluate how breast cancer risk factors (e.g., reproductive history, adiposity, physical activity, night shift work) and key dietary exposures (e.g., alcohol, fruit/vegetable intake, coffee consumption) influence microbial signatures in 8,000 participants with existing shotgun metagenomics data, with attention to timing and duration of exposures. This innovative proposal brings together an interdisciplinary team of experts, along with the rich resources of a well-established cancer epidemiology cohort, to thoroughly investigate the role of the GUT microbiome in breast cancer. By clarifying microbial pathways, linking them to hormonal and immune mechanisms, and identifying modifiable determinants, our work will address critical gaps in breast cancer etiology. Findings from this first large-scale prospective epidemiological study in the US on GUT microbiome and breast cancer incidence may guide microbiome-targeted prevention strategies and inform interventions to reduce breast cancer risk.