What would be the prognosis for stage 4 CCL?

So my dad recently found out he had CCL. It's stage 4 they say by all his swollen lymph nodes everywhere. He's done all his testing (bone marrow biopsy, tons of blood tests, removed a lymph node and tested it.) They just did a pet scan to make sure with all the swollen lymph nodes in his abdomen it wasn't morphing into ritchters syndrome and it came back fine. He's supposed to start chemotherapy next week I'm just curious what his prognosis would maybe be? The doctors said 1-5 years. I'm just wondering if it's different because it's so far along or looking for more information. Anything would help. Thanks!