For small biotech companies to be candidates for long term hold, the key is to have technology platform in my opinion to help minimize risk.
My current top picks are MNTA, MITI. I like the following as well for similar reason, but they are not as cheap: PLX (similar to MNTA in a way), SGEN (similar to MITI). There are others I like as well, but I would not put them as long term hold candidates.