Long-term follow-up of 241 patients with monoclonal gammopathy of undetermined significance: The original Mayo Clinic series 25 years later

OBJECTIVE: To determine the long-term outcome of patients with monoclonal gammopathy of undetermined significance (MGUS). PATIENTS AND METHODS: We reviewed the medical records of 241 patients with MGUS who were examined at the Mayo Clinic in Rochester, Minn, between January 1, 1956, and December 31, 1970. RESULTS: Follow-up was 3579 person-years (median, 13.7 years; range, 0-39 years). Only 14 patients (6%) were alive and had no substantial increase of M protein at last follow-up; 138 patients (57%) died without evidence of multiple myeloma or a related disorder; a malignant lymphoplasma cell proliferative disorder developed in 64 patients (27%). The interval from diagnosis of MGUS to diagnosis of multiple myeloma or related disorder ranged from 1 to 32 years (median, 10.4 years). CONCLUSIONS: The median survival rate of study patients with MGUS was only slightly shorter than that of a comparable US population. Risk of progression of MGUS to lymphoplasma cell malignancy is indefinite and persists even after more than 30 years of follow-up, with no reliable predictors of malignant evolution.