I found this article on the correlation between muscle mass and prognosis in people with cancer.
It doesn't mention CLL specifically though Non-Hodgkin Lymphoma does get a mention. The take home message is that low muscle mass worsens your prognosis.
If you need inspiration, go to the YouTube channel for a remarkable young lady called Emily Hayward. She was a personal trainer who survived 8 years with meta-static melanoma that had spread into her brain. It mentions in one or two of her videos that the doctors were amazed at her resilience. Her positive upbeat attitude throughout her ordeal is also worthy of admiration. Few people with brain tumors dead lift 130 kg!!! Her videos are here: