Multiple myeloma is diagnosed based on major criteria including a bone marrow plasmacytosis of at least 30% or an M protein level of over 3.5 g/L, or one major criterion and one minor criterion, which include a plasmacytosis between 10-30% or lytic bone lesions. The two key indicators for prognosis in multiple myeloma are tumor burden and proliferation rate, which can be predicted by levels of C-reactive protein and beta-2 microglobulin, with survival rates of 54 months if both are under 6 mg/L, 27 months if one is under 6 mg/L, and 6 months if both are over 6 mg/L.