Q: What is the famous "CRAB" for Multiple Myeloma (MM)?

Answer: CRAB symptoms are considered to be diagnostic of MM with evidence of proliferation of monoclonal plasma cells in the bone marrow.

C = HyperCalcium
R = Renal failure
A = Anemia
B = Bony lesions


Reference: 

International Myeloma Working Group (2003). "Criteria for the classification of monoclonal gammopathies, multiple myeloma and related disorders: a report of the International Myeloma Working Group". Br. J. Haematol. 121 (5): 749–57.