Hey Jim James,
You can come up with your own probability for success. Mine is around 80%. The downside is pretty clear. The upside could be an MC > $1B. Some would say much greater. You can come up with your upside.
Then you can decide the best way to invest for you. For me, it's currently about 15% of my investments. Failure? I'm OK. Success? I'm going great, cancer patients have a great new treatment with few side effects and the hope of living longer.
What's your investment strategy?
Good luck to Patients, NWBO, and Longs