As has already been stated you can use the prior tissue to better individualize current treatment. For example I'm a really rare patient, most people in my situation are already dead by this point in their treatment. Chemotherapy worked so well most of my primary tumor was gone within days and they haven't seen it since my 6th treatment. They still think it's there but it's generally too small to be seen. They didn't save the samples from my cancer to figure out why it worked so welln or why I've been able to handle aggressive treatment for far longer than average with minimal side effects. No hair loss, minimal nerve damage, etc. If that information could help even one other person, I would want it out there. I've contributed to every study I can be a part of and consented to every bit of sharing of my generic material I could, I only wish I could do more. Nearly everyone with my same diagnosis at the same time as me is dead. Speaking just for myself, being able to contribute to keeping other people from ever going through this means the world to me.