In this month’s issue of Blood, researchers report that ionizing radiation is associated with an elevated risk of monoclonal gammopathy of undetermined significance (MGUS), but that radiation does not lead to progression of the disease to multiple myeloma.

MGUS is a benign condition that affects the plasma cells. Like multiple myeloma, the disease is characterized by elevated levels of the antibody called monoclonal paraprotein, or M-protein. In multiple myeloma these protein levels are significantly raised and other symptoms begin to appear such as bone lesions and elevated calcium levels.

Researchers suggest that MGUS often precedes the development of multiple myeloma, though the cause of transformation is still unknown.

Besides age, sex, race, and family history, no consistent external risk factors have been clearly linked to multiple myeloma. Previously, individuals exposed to radiotherapy and atomic bomb survivors have not been found to be at excess risk of developing myeloma.

In the past, a few studies have evaluated the link between ionizing radiation and MGUS. MGUS incidences were not significantly associated with radiation dose, and MGUS leading to multiple myeloma did not occur at a significantly higher rate.

In the largest investigation that has looked at the effect of radiation exposure on MGUS development, researchers found that individuals exposed to radiation doses at ages 20 years and below had significantly higher risk for MGUS compared to those exposed at 20 years or older. Over 52,000 survivors from the surrounding area of the Nagasaki atomic bomb attack were tracked in the study, with 2.1 percent developing MGUS.

However, when evaluating the risk of developing multiple myeloma from MGUS, there was no correlation regarding radiation exposure. Of those who developed MGUS, progression to myeloma was found in 4.1 percent of people. This value was not found to be statistically significant compared to the annual risk of the disease progressing to myeloma of approximately 2 percent.

These findings indicate that ionizing radiation exposure may play a role in plasma cell disorders. Since plasma cell disorders are not fully understood, this observation could potentially help discover the biological mechanisms involved in multiple myeloma.

For more information, refer to this month’s issue of Blood ^[1] and an associated commentary ^[2].