Is Bisantrene's success or failure really tied to a test though?...

Is Bisantrene's success or failure really tied to a test though? If it is this is the first I've heard that.

For example, Dr. T. recently stated here that Keytruda works in 10% of most cancers, and that is one of the biggest selling cancer drugs.

Assuming there are no major negatives from giving Bisantrene to the 'wrong' patients (which as I understand it from historical trials, there does not appear to be), if anything, an accurate diagnostic test may only work to limit sales. Sure, it could increase the percentage of successful treatments (by minimising treatments given to people who are unlikely to be successful candidates), but would this allow the cost of the drug to be increased correspondingly so as not to have an overall negative effect on revenue?

But also having a test that excludes certain patients from treatment would have ethical consequences. If you consider that a test is unlikely to be 100% accurate - it may only indicate a higher or lower probability of success, as well as the fact there would be false positives and negatives, where would you draw the line over who gets treated and who doesn't? If you were a patient with limited treatment options, should you be denied access to a potential lifesaving treatment because you had a test indicating it had only a 10% chance of working instead of a 90% chance if your cancer was different?

And even then the definition of 'success' for a patient is all shades of grey too - it's unlikely to be a binary outcome of 'complete cure' vs 'no improvement in survival time', but anywhere along the spectrum of those two outcomes.

If there are tests and diagnostics being worked on, I would think that they would be used from the perspective of understanding in detail the mechanisms of exactly how Bisantrene works, gathering data that supports various approvals, as well as further research into improving treatment outcomes, rather than selection/exclusion of patients for treatment.