Risk of infections in multiple myeloma. A populationbased study on 8,672 multiple myeloma patients diagnosed 2008-2021 from the Swedish Myeloma Registry.

In multiple myeloma (MM), advancements in treatments and toxicity management have enhanced survival rates. This, coupled with shifting age demographics in MM, necessitates an updated assessment of infection risks in MM patients compared to the general population. Using Swedish population-based registries, we investigated the incidence of infections in 8,672 Swedish symptomatic MM patients diagnosed 2008-2021 and 34,561 matched controls. Overall, MM patients had a 5-fold risk (hazard ratio [HR] =5.30; 95% confidence interval [CI]: 5.14-5.47) of developing a clinically significant infection compared to matched controls. Bacterial infections represented a 5-fold (HR=4.88; 95% CI: 4.70-5.07) increased risk, viral and fungal infections 7-fold compared to controls. The first year after MM diagnosis the risk of infections compared to controls was 7-fold (HR=6.95; 95% CI: 6.61-7.30) and remained elevated up to 5 years after the myeloma diagnosis. The risk of infection compared to controls remained 5-fold in MM patients with follow-up till 2022. Preceding MM diagnosis, the risk compared to matched controls was significantly increased up to 4 years before MM diagnosis (HR=1.16; 95% CI: 1.05-1.28). Among MM patients, 8% had died within 2 months of diagnosis and infection contributed to 32% of all deaths. After 1 year, 20% MM patients had died, and infection-related mortality was 27%. Our data constitute the largest population-based study to date on the risk of infections compared to the normal population in the era of modern MM therapies and confirms that infections still represent a major threat to patients and underscores importance of preventive strategies.