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Older rules set by the FDA for chemo drugs have in the past (& maybe still now if they are still enforced) tended to negatively affect the true potential of some drugs in trials. This is the case of antiangiogenesis drugs which are usually slow acting & may only work as cytostatic rather than cytotoxic agents.
One of the rules was to drop from a trial any patient showing a 50% rise in tumor size even if his markers were indicating drug activity & others in the same trial were showing even more benefits.
So final trial statitics based on such rules would result in a poor response rate not to speak of the patient with advanced disease left out without treatment which may otherwise prolong life if sustained over a longer time.
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