Association between post-diagnostic use of cholera vaccine and risk of death in prostate cancer patients https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6006429/

"We found that patients with prostate cancer, who had used cholera vaccine after their cancer diagnosis, had a 43% decrease in prostate cancer mortality and a 47% decrease in overall mortality, as compared to patients who did not use cholera vaccine. The decreased mortality rate associated with cholera vaccination was largely consistent, irrespective of the patient’s age or tumor stage at diagnosis, and other potential confounders, including disposable income. Mortality reductions were also noted in several sensitivity analyses. Our findings suggest that cholera vaccine is associated with a reduced mortality rate in patients with prostate cancer."

"In this population-based study, we suggest that subsequent administration of cholera vaccine after prostate cancer diagnosis might reduce the mortality rate."

"Excessive bacterial growth was observed in the small intestine among children who received cholera vaccine29, which suggests that intestinal microbiota might be altered after oral cholera vaccination. As intestinal microbiota might play an important role regarding antitumor immunity30,31, cholera vaccination might protect against the progression of prostate cancer by alternating intestinal microbiota."

Similar results were found in Colorectal Cancer https://www.ncbi.nlm.nih.gov/pubmed/28923497