To my mind, the
starting point is that even in viscerally metastatic settings, endocrine
monotherapy can be effective. Even combinations of endocrine agents (AI+SERM) may be effective. And there is a fair amount out there to support certain chemo/endocrine and biological/endocrine therapies as synergistic.
I have heard that endocrine therapies by themselves may take longer than chemos to show measurable effect. So perhaps cell assays are too brief to emulate that scenario.
But if it were possible to know in advance the likelihood that (generally) lower toxicity endocrine therapy could give benefit, that would be a big help to many.