Very small sample size and only in mice. Most experimental treatments don't make it to the clinic, and this could be another in a long list of exciting early results that don't lead to anything. However... These results seem too good to be true, but the paper actually seems pretty good. There have been other attempts to use anaerobic bacteria to treat cancer (as solid tumors tend to be hypoxic environments), this is the first I've seen that interacts with PD-1/PD-L1 pathway. This is the most promising cancer treatment I've seen in quite a while. Maybe we can be cautiously optimistic!