| − | The M protein is an antibody or part of an antibody found in unusually large amounts in the blood or urine of people with multiple myeloma and other types of plasma cell tumors. It is also called monoclonal protein. | + | The M protein was a antibody or part of a antibody found in unusually large amounts in the blood or urine of people with multiple myeloma and other types of plasma cell tumors. It was also called monoclonal protein. |