Second primary malignancies (SPM) in African American (AA) and white patients with multiple myeloma in the National Veterans Affairs (VA) healthcare system.
Authors: Premji Sarah , Yildirim Cenk , Fillmore Nathanael , Yellapragada Sarvari , Brophy Mary T. , Do Nhan , Huang Quillan , Friedman Daphne Ruth , Munshi Nikhil C. 
Published: June 2021

10507 Background: In the recent decade, novel therapies have led to significant improvements in overall survival (OS) in symptomatic multiple myeloma (MM). With this increase in OS, there is an increase in the incidence of second primary malignancies (SPM) in patients with MM. This is related to multiple factors; we hypothesize that racial disparities also play a role. There is a paucity of studies with large, high quality datasets evaluating racial disparities in SPMs in MM. Our goal is to explore patterns of incidence of SPMs in US Veterans with MM, focusing on racial disparities. Methods: We conducted a retrospective cohort study based on electronic health record (EHR) and cancer registry data recorded in the VA’s Corporate Data Warehouse (CDW) between January 1, 1999 and January 1, 2018. We compared incidence of SPMs (defined as malignancies occurring after the diagnosis and treatment initiation of MM) using the standardized incidence rate ratio (IRR). Univariate and multivariable analyses were performed, using a Cox model adjusting for age, race, gender, treatment era, smoking status, and stage at MM diagnosis. Results: There were 8467 Veterans (97.4% male) with MM identified with self-reported race: White, 5029 (59.4%); AA, 2178 (25.7%); and other or unknown, 1260 (14.9%). At 7.5 years of follow up, 430 (5.1%) MM patients developed SPM while 8037 did not. 982 had received HSCT (Hematopoietic Stem cell transplant) of whom 65 (6.62%), a significantly higher proportion developed SPM versus those without HSCT (n = 7485) of whom 365 (4.87%) developed SPM (p = 0.024). Among those Veterans who had SPM 380 (88.3%) had solid tumors, 50 (11.6 %) had hematological malignancies. Of 88.3% with solid SPM the distribution was: prostate cancer, 113 (29.7%); digestive tract cancers, 63 (16.6%); lung cancer, 55 (14.4%); and GU (bladder/renal/testicular), 48(12.6%). The cumulative incidence of developing SPM increased steadily over time for the duration of this study period of 7.5 years from diagnosis. The median age of diagnosis for Whites was 68.2 years and for AA was 64.3 years, (p < 0.001) demonstrating that MM occurred earlier in AA. The hazard ratio for AA versus whites to develop SPMs was 1.21 (0.975-1.505) (p = 0.0823). However, the risk of prostate cancer was significantly higher in AA with an adjusted hazard ratio of 1.81 (1.196-2.739) (p = 0.005). No racial disparities were observed in the incidence of other types of SPMs. Conclusions: Our study suggests that the risk of SPMs does not plateau over a patient’s lifetime. HSCT was found to be an independent predictor of SPM, while smoking and agent orange were not. Our cohort is one of the largest groups of AA with MM in published literature. AA did not have a higher incidence of SPMs overall; but had a significantly higher incidence of prostate cancer than whites. We hope to develop an individualized predictive model for SPM in patients with MM.