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Breast cancer

Compared within 3 studies that had both: 673 people with breast cancer and 598 healthy people. 33 genera are less common in people with breast cancer, and 4 more common.

A difference is an association: it doesn’t mean these genera cause, prevent or treat breast cancer. GMrepo reports this group at the genus level only, so these are genera, not species.

Phylum

Searching opens both lists and shows only matching rows.

Less common in breast cancer · 33

Strongest first, then the biggest gap · Each figure is 10 people Strongest first · Each figure is 10 people
  1. Lachnospira genus in 3 studies Healthy 74% breast cancer 50%
  2. Romboutsia genus in 3 studies Healthy 70% breast cancer 46%
  3. Agathobacter genus in 3 studies Healthy 82% breast cancer 61%
  4. Catenibacterium genus in 3 studies Healthy 47% breast cancer 27%
  5. Holdemanella genus in 3 studies Healthy 58% breast cancer 39%

More common in breast cancer · 4

Strongest first, then the biggest gap · Each figure is 10 people Strongest first · Each figure is 10 people
  1. Parasutterella genus in 3 studies Healthy 24% breast cancer 40%
  2. Thomasclavelia genus in 3 studies Healthy 36% breast cancer 50%
  3. Atopobium genus in 3 studies Healthy 1.0% breast cancer 4.5%
  4. Eggerthella genus in 3 studies Healthy 9.2% breast cancer 17%

As many carry these · 1 the amount differs

Strongest first, then the biggest gap · Each figure is 10 people Strongest first · Each figure is 10 people
  1. Prevotella genus in 3 studies Healthy 81% breast cancer 77%

    Carriers have about a third as much, in 2 of 2 studies (31% → 9.1% of their gut microbes).

Where these numbers come from

Studies
Only GMrepo projects that had people with the condition and healthy people, 10 or more of each. Numbers come from those studies, never from pooling.Sampled in Ghana, the United States.
How common
The share of people whose sample has any of it, in the people with the condition and in the healthy people of those same studies. Tested within studies (Cochran–Mantel–Haenszel, corrected for testing many microbes); a difference counts when it is clear and meaningful (Cohen’s h of 0.2 or more).
Strength word
Counted by code from how many studies point the same way: Seen again and again (3 or more, none clearly the other way), Seen more than once (2, the majority), Seen once (1, listed last). Where studies disagree, a row isn’t listed.
Each study
Tap a row for every study’s own numbers, and for how much carriers have.
Analysis
Our analysis of GMrepo data. GMrepo on Data sources · Read the rules

Also compared · 145 genera

Compared within studies that had both, but not listed above.

Studies disagree · 7

No meaningful difference · 138
PubMed · human studies and reviews first

Recent research

All research on it
  1. Randomized trial Cancer prevention research · 2026
    Weight Loss and Omega-3 Supplementation Modulate the Microbiome in Women with Increased Breast Cancer Risk.
    PubMed ↗
  2. Randomized trial Cancer reports · 2026
    Dance and Dietary Intervention Improves Metabolic Health, Fitness, and Quality of Life With Modest Gut Microbiota Shifts in Breast Cancer Patients With Obesity: A Pilot RCT.
    PubMed ↗
  3. Review International journal of molecular sciences · 2026
    The Role of Selected Bacteria in Breast Cancer Initiation and Development.
    PubMed ↗
  4. Review Current problems in cancer · 2025
    Unraveling the microbiome's role in breast cancer progression and treatment response.
    PubMed ↗
  5. Review Gut microbes · 2025
    Interaction between the breast tumor microenvironment and gut microbiome.
    PubMed ↗

Source: PubMed, U.S. National Library of Medicine · 50 linked papers, last 10 years