Cholera vaccine and cancer

Someone brought to my attention, that the oral cholera vaccine, Dukoral, reduces the rate of death in patients diagnosed with colorectal cancer by 47%.

https://www.ncbi.nlm.nih.gov/pubmed/28923497

Ok, cholera, being an affliction of the intestines, sounds logical. The vaccine being an oral drug should first impact the intestinal tract. Sounds logical that it would have potential to impact tissue in direct contact with the vaccine.

So it got me wondering about whether it had any effect on other cancers. I couldn't find any study on breast cancer, but a similar hormone driven cancer, prostate cancer has a similar benefit:

https://www.ncbi.nlm.nih.gov/pubmed/29915319

Abstract

Recent evidence suggests that cholera toxin might have multiple functions regarding the ability to regulate the immune system. However, it is unknown whether subsequent administration of cholera vaccine might affect the mortality rate in patients with prostate cancer. Here we report that patients in Sweden, who were diagnosed with prostate cancer between July 2005 and December 2014 and used cholera vaccine, have a decreased risk of death from prostate cancer (HR, 0.57; 95% CI, 0.40-0.82) as compared to patients with prostate cancer but without cholera vaccine use, adjusted for a range of confounding factors. In addition, patients using cholera vaccine show a decreased risk of death overall (HR, 0.53; 95% CI, 0.41-0.69). The decreased mortality rate is largely consistent, irrespective of patients' age or tumor stage at diagnosis. In this population-based study, we suggest that subsequent administration of cholera vaccine after prostate cancer diagnosis might reduce the mortality rate.

Once again a 47% reduction in rate of death for those with prostate cancer who took the vaccine, post diagnosis. Now we are on to something. There is no proximal relation between the prostate and the intestinal tract, which would be impacted by an oral vaccine made of deactivated cholera and bacteria. The mode of operation has to be something more system, such as immune boosting.

Isn't there a possibility that the same impact might be made with respect to breast cancer? The two are both hormonally driven. Both share some gene mutations. Got me thinking. Anyone have any insight into this? Or know of any research done that would show the statistical impact of the cholera vaccine on breast cancer patients? I wonder what drove the researchers to look into the connection to prostate cancer? Why not breast?