Other forums on this platform do mention Fucoidan, but nothing relevant to prostate cancer, it seems to me.
The clinical trials site shows 16 studies with Fucoidan, some are cancer related, but none mentions prostate cancer.
https://clinicaltrials.gov/ct2/results?cond=&term=fucoidan&cntry=&state=&city=&dist=One can also enter BAX513 which appears to be a certain formulation of fucoidan. That entry yields one phase 1 study, not relevant to prostate cancer either.