I can tell you my history - it would be inappropriate to discuss anybody elses history here.
When I got a CLIPPERS diagnosis I was told there was a slight possibility that I could in fact have a diffuse CNS lymphoma even though there was nothing found on any of the various tests I had. I declined a brain biopsy which might have picked it up (but also it might not have done). I was told this kind of Lymphoma was very rare and hard to diagnose - but then CLIPPERS is also very rare and hard to diagnose.
I "held my breath" for several months as I was told Lymphoma would appear to initially improve with steroids but would then come back. I wrote a blog entry at the time about Lymphoma being "the elephant in the room". This is one reason why stronger diagnostic criteria and definitive tests are needed for CLIPPERS.