Some of the best-performing biopharma stocks in recent years belong to companies developing cancer drugs, and it looks as if this trend is going to continue throughout 2017 and into the foreseeable future. Estimated global spending for oncology medicines is expected to grow from $107 billion in 2015 to $150 billion by 2020 as life spans lengthen across the developed world.There are hundreds of biotech start-ups attempting to develop the next breakthrough therapy, but investors can avoid a great deal of risk by focusing on companies with winning track records and clear paths to continued growth.