Can probiotics help prevent diarrhea from breast cancer medication?

Neratinib is a targeted cancer medication that helps treat HER2-positive breast cancer, but it commonly causes severe diarrhea that can interrupt treatment. This study tests whether taking probiotics — beneficial bacteria that support gut health — can reduce or prevent this side effect. Researchers will compare women who receive probiotics with those who receive a placebo (an inactive pill), and all participants will also receive standard anti-diarrhea medication.

Severe diarrhea from this medication causes many patients to skip doses, reduce their dose, or stop treatment entirely, which can impact how well the cancer therapy works. Early evidence suggests that probiotics might help by supporting a healthy gut microbiome, but doctors don't yet know if this actually prevents diarrhea from this specific medication.