A condition characterized by the presence of a monoclonal gammopathy (MG) in which the clonal mass has not reached a predefined state in which the condition is considered malignant. Up to 25% of cases of monoclonal gammopathy of undetermined significance (MGUS) progress to a B-cell malignancy or myeloma. MGUS may occur in conjunction with various carcinomas, chronic inflammatory and infectious conditions, and other diseases.