Researchers at City of Hope are focusing on a growing area of cancer research: the gut microbiome. New findings presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting suggest that changing the bacteria in the digestive system could help people with advanced kidney cancer respond better to immunotherapy.
The study examined a live bacterial product, CBM588, and the potential influence of a patient’s gut microbiome on treatment outcomes.
Why the Gut Microbiome Matters in Cancer
Scientists are discovering that the gut microbiome plays a key role in the immune system, inflammation, and even how well some cancer treatments work.
“Microbiome-directed interventions should be at the center of this transformative era in kidney cancer,” Dr. Rahul Winayak, postdoctoral research fellow at City of Hope, tells BlackDoctor.
Previous studies have found links between gut bacteria and cancer treatment outcomes. Now, researchers are investigating whether intentionally changing the microbiome could help patients respond better to therapy.
The City of Hope team analyzed data from two early-stage clinical trials involving patients with metastatic renal cell carcinoma, the most common type of kidney cancer.
Researchers tested CBM588, a live bacterial product, together with standard first treatments for kidney cancer:
They aimed to determine whether adding CBM588 could help patients respond better to treatment and slow cancer progression.
What Did Researchers Find?
The results were encouraging.
Patients who received CBM588 alongside standard treatment experienced:
Although these trials were small and still in the early stages, the findings suggest that altering the gut microbiome could help immunotherapy work more effectively.
“We showed quite a profound progression-free survival response with patients who received the live bacterial product,” Dr. Winayak says.
One of the most interesting findings was dysbiosis, an imbalance in the gut microbiome.
Researchers used a microbiome assessment tool called the TOPOSCORE to group patients by the types of bacteria in their digestive systems.
Patients with higher levels of the bacteria associated with worse immunotherapy outcomes seemed to derive the greatest benefit from CBM588.
The researchers believe this means that therapies targeting the microbiome could be especially helpful for patients whose gut bacteria make them less likely to respond to immune checkpoint inhibitors.
Not yet, but researchers think it could become an important tool in the future.
Currently, microbiome testing requires advanced genetic sequencing of stool samples, which can take several weeks. This long wait makes it difficult to use in everyday medical care when clinicians need to make quick decisions.
However, researchers noted that new developments have made the process faster, with a lab test that can provide results in just 48 hours.
If future studies confirm these results, clinicians may one day use microbiome testing to help select treatments or identify patients who could benefit from microbiome-based therapies.
“We may even enter a scenario where we can screen patients prior to treatment,” Dr. Winayak adds. “Then we can look at potential interventions, whether that’s diet, a high-fiber diet, or other approaches alongside therapy.”
Today, CBM588 is still being researched and is not yet a standard treatment for kidney cancer. However, these findings show that factors beyond the tumor itself can affect how well treatment works.
Researchers are beginning to believe that lifestyle factors such as diet, exercise, antibiotic use, and gut microbiome health may all influence how patients respond to immunotherapy.
For clinicians, this research does not mean that you should advise patients to change their diet or that taking probiotics can replace cancer treatment. Instead, it suggests that in the future, you may be able to personalize their treatment based on both the tumor’s genetics and the microbiome’s biology.
This field of research is moving forward quickly.
A Phase 3 trial of CBM588 in combination with immunotherapy is now underway. If successful, it could be one of the first major studies to show that targeting the microbiome can improve cancer treatment results.
Meanwhile, City of Hope and other cancer centers are expanding microbiome research into additional areas, including:
“I think the microbiome is moving beyond just being an associative factor in cancer therapy,” Dr. Winayak says. “It’s now becoming something that we can really think about as a therapeutic target.”
The ASCO 2026 results add to the growing evidence that the gut microbiome may play an important role in the success of cancer treatment. More research is needed before microbiome testing or bacterial therapies become common, but these early results suggest that targeting gut bacteria could one day help people with advanced kidney cancer.
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