"The patient is the one with the disease" - the Fat Man
In all seriousness, it's obviously a crappy part of our career. Many other fields deal with similar poor outcome situations, often times worse than we do in many ways. I try to find to comfort myself that I (and the patient) made the best calls we could with the information we had at the time. You didn't fail your patient, the R-CHOP (or FOLFOX, AC->T etc.) did.