No. 1: Ziopharm Oncology ( NASDAQ:ZIOP)
Biotech companies including Ziopharm Oncology are conducting a flurry of research into medicines that super-charge the immune system against cancer, but the market for immuno-oncology has become very crowded in the past two years and the jury is still out on whether or not these promising approaches will be effective and safe.

That's especially true of Ziopharm Oncology's pipeline because its most advanced drug is in phase 1 trials for breast and brain cancer -- the earliest stage for human trials -- and its work on chimeric antigen receptor T-cell therapies isn't in human trials yet.

Granted, the company is collaborating with top talent at the MD Anderson Cancer Center and its use of switching technology could help it craft a best-in-class option, but there's a lot of question marks regarding life threatening cytokine responses popping up in the study of CAR-T and an argument could be made that competitors, including Juno Therapeutics(NASDAQ: JUNO) have programs that could reach the market more quickly than Ziopharm Oncology's.

Obviously, I'll be rooting for Ziopharm Oncology's research to pan out, but it's too early in its trials for me to be willing to take on the risk of a clinical trial stumble or its being outmaneuvered by competitors.