I just searched on B12 affect on PCa on a couple chatbots. In a meta-analysis it looks like high levels of B12 don't reduce or slow PCa; most studies show no effect, but a couple studies show that B12 could worsen aggressive PCa a bit (OR 1.17 and one study OR 1.5ish, I think). I was low a year ago and started taking it. My PCa persists so I'm going to do a blood test and to be safe, will likely reduce or stop taking B12 myself. It doesn't look like it's a huge factor but my rule now is that I won't take any supplement or food, even if some studies show benefit, where respectable other studies show that it may make PCa worse (i.e Vit. E, selenium in brazil nuts, etc). There's a lot they don't know about diet, vitamins, and supplements still, so I'm trying to play it safe. And interactions are really hard to predict.