Science1 publisher3 min readPublished
Distinct gut microbes mark colorectal and breast cancers diagnosed at 50 or younger
Mayo Clinic researchers tie colorectal and breast cancers diagnosed at 50 or younger to distinct gut microbes, using stool from 1,364 patients. The signals give researchers named bacteria to test next, though the data cannot yet say whether those microbes drive early disease or follow from it.
The Scientist · Science desk
What happened
- Brain cancer, the third cancer in the early-onset analysis, showed no comparable age-related microbiome differences.
- Measured against 287 people without cancer and adjusted for other health conditions, 341 bacterial species tracked with five cancer groups.
- Stool was collected before any new treatment began and linked to each patient's clinical records on side effects and outcomes.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- decision Labs choosing which gut bacteria to test for a causal role in early-onset cancer now have named first candidates: V. parvula for colorectal and C. scindens for breast.
- constraint A stool screen for early-onset risk would need samples taken before diagnosis; this cohort was sampled after diagnosis, so it cannot show that the signatures come first.
- capability Pairing baseline stool with later side-effect records lets the cohort test whether a patient's pre-treatment microbiome predicts who will have adverse events.
The early-onset comparison is made inside each cancer type: patients diagnosed at 50 or younger against patients with the same cancer diagnosed later in life [15]. That holds the disease fixed and lets age at diagnosis vary, so age itself remains a possible explanation for any gap in gut bacteria. The brain cancer result is the study's best answer to that [9]. If being under 50 were enough to produce the colorectal and breast patterns, I would expect some trace of it among younger brain cancer patients too.
The non-cancer comparison group is small beside the 1,364-patient cohort [1], about one person without cancer for every 4.8 patients [1]. The GEN report does not give the size of the early-onset colorectal and breast subgroups. Those counts set how much confidence a difference spread across 64 species deserves.
The colorectal finding has a plausible chemical link, and the link can run in the opposite direction. Tumors can produce high levels of lactate, and V. parvula uses lactate to grow [7]. On that account the tumor feeds the bacterium, and the microbe is a marker of the cancer more than a driver. According to the report, whether the relationship plays a role in early-onset disease is not yet known [7]. The breast cancer measurements converge on bile acids. Clostridium scindens, one of the 64 species that differed, is involved in bile acid and steroid metabolism, and the same patients had lower primary bile acids [8].
The authors state that the findings do not establish that these differences cause early-onset disease [11]. They built the analysis to rank candidates. "As the field shifts from association to causality, a key challenge is prioritizing microbes and pathways most likely to drive specific cancers," they wrote [13]. Ruben Mars, a Mayo Clinic microbiome researcher and co-corresponding author [3], said: "We can now narrow the search to those microbial changes that are most specific to individual cancers." [12] The ranking extends beyond age of onset. Neuroendocrine tumors showed a broad loss of common health-associated bacteria, liver and intrahepatic bile duct cancers had more Enterococcus faecalis, and esophageal cancer had six elevated species including Streptococcus [6].
The reason to chase these leads is epidemiological. According to the American Cancer Society, colorectal cancer incidence is rising about three percent a year among adults aged 20 to 49, and breast cancer incidence 1.4 percent a year among women under 50 [10].
Collecting stool before treatment [2] means chemotherapy and other drugs cannot account for the baseline differences. The paper's title names treatment adverse events alongside cancer signatures [3]. The GEN account does not report which microbes went with which side effects. It does report survival associations, and they are observational like everything else here: specific gut bacteria tracked with survival in colorectal, liver and intrahepatic bile duct, ovarian and prostate cancers and melanoma, and Bifidobacterium longum went with longer survival in liver and bile duct cancer [14].
What to watch
- The Cell paper's adverse-event results: which pre-treatment microbes, if any, predict specific side effects, and whether they hold up in a second cohort.
- Studies that sample stool before diagnosis to see whether the early-onset colorectal and breast signatures appear before the cancer does.
- Causal experiments on V. parvula or C. scindens, and whether any effect seen in animal models carries over to people.