I think the trials take "forever" time. Not to mention that they also cost "forever" money. If the investors or regulators are not convinced by the researchers you may say the "breakthrough" is DOA
Trials generally have a very specific time frame during the initial setup. Investors don't invest into specific treatments but into the companies, which can often make or break the company. With cancer trials typically this is a few years of studies at most. If results are promising they tend to move forward quickly, otherwise studies end prematurely for patient safety if negative outcome is seen. Neutral results are not uncommon.