Some time ago, the FDA approved a drug based on tumour shrinkage...

Some time ago, the FDA approved a drug based on tumour shrinkage but when the drug stopped working, tumour growth actually accelerated. This explains why the FDA now requires approval to be based on Overall Survival, with Progression Free Survival (rather than tumour shrinkage) the surrogate end point for Accelerated Approval.

It might be technically correct to say that Stable Disease is not a 'response' in RECIST terms, but it IS a highly relevant term with respect to Progression Free Survival (and by implication, Overall Survival) - which is what counts with the FDA.

NOX66 + low dose ERBT stopped disease growth in its tracks for 40% of DARRT patients. These were elderly, frail men who had uncontrolled tumour growth despite multiple rounds of devastating therapy and yet, here they were six months later, with no tumour growth and, in at least one case, no pain at all. This was a fantastic result.