The Association of Agent Orange (AO) Exposure with Monoclonal Gammopathy of Undetermined Significance (MGUS) to Multiple Myeloma (MM) Progression: A Population-based Study of Vietnam War Era Veterans.

Background: Herbicide and pesticide exposure (e.g., agent orange [AO]) is associated with an increased risk of multiple myeloma (MM) due to the contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Monoclonal gammopathy of undetermined significance (MGUS) is the precursor state to MM; however, not all patients with MGUS progress to MM. It is unclear whether AO exposure increases the risk of progression of MGUS to MM. Purpose: We aimed to determine the association between AO exposure and progression to MM in a nation-wide study of U.S. Veterans with MGUS. Patients and Methods: This is a population-based cohort study of Vietnam Era Veterans diagnosed with MGUS. A natural language processing (NLP) algorithm was used to confirm MGUS and progression to MM. The association between AO and progression was analyzed using multivariable Fine-Gray subdistribution hazard model with death as a competing event. Veterans who served during the Vietnam War Era from 1/9/1962-5/7/1975 and were diagnosed with MGUS between 10/1/1999-12/31/2021 were included. We excluded patients with missing BMI values, progression within 1 year after MGUS diagnosis date, non-IgG or IgA MGUS, or birth years outside of the range of the AO exposed group, and race other than Black and White. AO exposure and service during 1/9/1962-;5/7/1975 and stratified according to TCDD exposure levels by three time periods: 1/9/1962-11/30/1965 (high), 12/1/1965-12/31/1970 (medium), or 1/1/1971-5/7/1975 (low). The association between AO and progression was analyzed using multivariable Fine-Gray subdistribution hazard model with death as a competing event. Results: We identified 10,847 Veterans with MGUS, of whom 7,996 had AO exposure. Overall, 7.4% of MGUS patients progressed to MM over a median follow-up of 5.2 years. In multivariable analysis, AO exposure from 1/9/1962-11/30/1965, high TCDD exposure, was associated with an increased risk of progression (adjusted hazard ratio 1.48; 95% confidence interval 1.02-2.16), compared to Veterans with no exposure. Conclusions: In patients with MGUS, the high Agent Orange exposure time period is associated with a 48% increased risk of progression to multiple myeloma. This suggests that patients with MGUS and prior Agent Orange exposure or occupational exposure to TCDD (eg. Agricultural workers) may require thorough screening for plasma cell dyscrasias.