Patients with a condition called monoclonal gammopathy of undetermined significance, characterized by the presence of the abnormal monoclonal or M protein, have a small but persistent risk of multiple myeloma or a related cancer, even after they’d been stable for 30 years, researchers found.
The study, “Long-Term Follow-up of Monoclonal Gammopathy of Undetermined Significance,” was published in The New England Journal of Medicine.
Monoclonal gammopathy of undetermined significance, or MGUS, is found in 3.2% and of people between 50 and 70, and in 5.3% of people 70 and older.
Previous small-scale studies reported that MGUS progresses into a blood cancer in 7% to 19% of patients after five to 10 years. But “the small numbers of patients or the short follow-up in these studies limit the reliability of these results,” investigators wrote.
Mayo Clinic researchers in Rochester, Minnesota, studied 1,384 MGUS patients to determine their risk of developing multiple myeloma or any related blood cancer. Patients had been diagnosed between 1960 and 1994, and were followed for a median of 34.1 years.
Among the participants, 54% were men. The median age at MGUS diagnosis was 72. In 15% of patients, the abnormal monoclonal protein was of the IgM subtype. The remaining — collectively included in the non-IgM subtype — had either IgG, IgA, or a mixture of two monoclonal proteins.
At the time of the analysis, 1,300 patients had died. Of the 84 who were still alive, the disease had progressed in five.
Interestingly, the risk for MGUS progression in the IgM group — 10.8 times higher than the general population — was higher than that seen in non-IgM patients — 5.7 times higher than the general population.
“Our study showed significant differences in the mode and risk of progression between patients with IgM MGUS and those with non-IgM MGUS,” researchers wrote.
And while the risk of progression of patients with IgM MGUS was 2% per year in the first 10 years after diagnosis, decreasing to 1% per year thereafter, patients with non-IgM MGUS showed no changes in the risk of progression during follow-up.
The results showed that the risk of progression was quite small — 1% per year — but persisted indefinitely. Compared to other general causes of death, the risk for progressing to blood cancer remained small.
Researchers also found that patients with MGUS live shorter lives compared to sex- and age-matched controls from the general population of Minnesota residents, but “the risk of progression to myeloma or a related disorder is much less than the competing risk of death due to other causes.”