This is the second paper I've read on the topic. I can't find the first one but it indicated that microbes related to sugar/refined carb consumption were higher in non-responders versuses those with more diverse microbiota resulting from a diet of healthier foods, lots of veggies.
So it seems what we eat can influence our cancer outcomes after all. A great reason to change your diet as early as possible as it may significantly improve outcomes, if immunotherapy is the route you wind up on. My guess is chemo and radiation aren't influenced by diet because of the way they work but newer treatments might very well be.
There are a few great books I know of on how to create a diverse microbiome. I can't quite recall them right now but I'll look them up later, if interested. You can influence your microbiota over a very short period.