Racial Disparities in Incidence and Survival for Patients with Multiple Myeloma in the United States

Background: Over the past two decades the incidence of myeloma has been gradually increasing in the United States. The incidence rates are higher in men than women, and higher in blacks than whites. Similar to the differential incidence, overall survival rate between blacks and whites are also dissimilar; a difference that is not completely explained and may be attributable to genetic variations between the two groups.

Methods: Using data from 18 SEER registries, we examined differences in incidence, mortality and survival from 1973-2012 for 89,867 myeloma patients (68,701 white, 16,364 black and 4,802 others) by race, gender and age-stratification. ICD-O-3 and morphologic (9732/3) codes were used to identify cases. Age-adjusted incidence and mortality rates, regression analysis and survival curves were calculated by race. Statistics were computed using the National Cancer Institute SEER*Stat software, version 8.2.0. and SAS software, version 9.4 (SAS Institute Inc, Cary, NC).

Results: Median age at diagnosis was 70 years (range 20-100 years) for the overall population (blacks: 66 years; whites: 71 years, and others: 69 years (P<0.01). The age-adjusted incidence rates per 100,000 populations were: blacks- 11.9 (95% CI 11.6, 12.1, P-value<0.05); whites- 5.1 (95% CI 5.0, 5.2) and others- 3.7 (95% CI 3.6, 3.9). The incidence rates were higher for black males, 14.2 (95% CI 14, 14.7) followed by black females, 10.3 (95% CI 10, 10.6, P-value<0.05).   Using white male as reference, incidence rate ratios for black males and females are 2.20 (95% CI 2.12, 2.28) and 1.60 (95% CI 1.54, 1.65) respectively. The 2-year relative survival rates (RSR) for the study population were: whites- 60.4%, blacks: 64.1% and others: 68.4%, respectively. The 5-year RSR by race and gender are included in figure 1. On the survival analysis, black race is an independent factor to have improved survival (HR=0.884, P-value<0.0001). This was corroborated on regression analysis, showing decreased hazard ratios for blacks (HR 0.856 95% CI 0.834, 0.878) compared to whites (P-value<0.001).

Conclusions: Black patients are diagnosed younger than whites and other races. The IRRs for black males are twice compared to white males.  While the 5-year RSRs are improving for all races and genders, black race is an independent factor to have improved survival. Further population-based studies focused on the exploring the underlying biological mechanisms of disease may explain the earlier presentation with disease and better overall survival among black patients.