THE NATURAL-HISTORY OF MONOCLONAL GAMMOPATHY OF UNDETERMINED SIGNIFICANCE - A 5-YEAR TO 20-YEAR FOLLOW-UP OF 263 CASES

Patients with monoclonal gammopathy of undetermined significance (MGUS ) have a serum monoclonal component (M-component), but no evidence of multiple myeloma, macroglobulinaemia, amyloidosis or other plasma cell proliferative disease. A long-term follow-up study(median 11.5 years) has been carried out in 263 cases of MGUS, 159 males (60.5%) and 104 females (39.5%), aged 40-89 years (median 66.5 years). The actuarial p robability for malignant transformation was 6.1, 15.4 and 31.3% at 5, 10 and 20 years, respectively. At the final evaluation, 157 patients(5 9.7%), 119 (45.3%) of whom with no increase and 38 (14.4%) with an inc rease in serum M-component, died of causes unrelated to MGUS and witho ut development of any plasma cell proliferative disease; 47 patients ( 17.9%) were still alive without increase in M-component; Il patients ( 4.1%) were still alive and at follow-up presented values of serum M-co mponent >30 g/l without any evidence of plasma cell proliferative or l ymphoproliferative disease; 48 patients (18.3%) developed multiple mye loma (35 cases, 13.1%), solitary plasmacytoma of the bone (2 cases, 0. 8%), macroglobulinaemia (4 cases, 1.6%), malignant lymphoma (3 cases, 1.2%), amyloidosis (2 cases, 0.8%), chronic lymphocytic leukaemia (1 c ase, 0.4%), and plasma cell leukaemia (I case, 0.4%). The patients dev eloping multiple myeloma, solitary plasmacytoma, macroglobulinaemia an d plasma cell leukaemia had an increase in serum M-component, whereas no increase was found in malignant lymphoma, amyloidosis and chronic l ymphocytic leukaemia. These findings and the data in the literature su ggest that MGUS could be considered a preneoplastic condition; since n o clinical and laboratory features are able to identify in advance the patients at high risk of disease progression, each patient must be fo llowed up indefinitely.