Hi NJ,
CTC is trial stuff only as far as I know. Mine was part of a trial. They couldn't find any !
You could try the Royal Marsden to ask your question.
I think the John Hopkins clinic in the U.S. is looking at a gene mutation which helps guide on Enzalutamide working or not. But haven't heard of anything else here.
Your GP will be able to guide on costs I would think for private purchase of either. I'd suggest it might be better to buy the med if you can't get it on NHS & try it for say two months to see if it works. Rather than expensive & possible unreliable tests ? It's certainly not an ideal situation !