Solitary Plasmacytoma Incidence, Mortality, and Survival Trends in the United States
Authors: Bikmal Anirudh , Radhakrishnan Lakshmi , Nooka Ajay K. 
Published: October 2019

Abstract
Background: The trends of incidence of solitary bone plasmacytoma (SBP) varied over time due to the changing definitions and the absence of clarity of the criteria. Prior studies have attempted to identify factors such as older age, gender, race as prognostic factors that influence survival of patients with SBP, but with changing paradigm of myeloma treatments, there is limited literature regarding the incidence, mortality and survival trends of SBP.
Methods: We used the SEER registry from 1973-2009 to evaluate the incidence, mortality and survival trends in patients with SBP. The results were reported as crude incidence, mortality and survival rates. Two-sample t-tests, ANOVA as well regression analysis were used to examine correlation. 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). Using the ICD-O-3 and morphologic codes of 9731/3 to identify cases, the final study cohort consisted of 2,734 cases. Trends were evaluated by the eras of diagnosis: 1973-1980, 1981-1985, 1986-1990, 1991-1995, 1996-2000, 2001-2005, and 2006-2009. Age-adjusted incidence rates (IR), standard mortality rates (SMR), survival rate (SR) were expressed as new cases per 100,000 person-years, and age-adjusted to the 2000 US standard population.
Results: The median age of diagnosis of SBP among blacks is 61 years (range, 21-91) compared to others: 60 years (range, 28-88) and whites: 66 years (20-97). The age adjusted incidence rates for black males is: 0.3 (95%CI 0.2, 0.3) followed by black females 0.2 (95%CI 0.1, 0.2) white males 0.2 (95%CI 0.2, 0.2) white females 0.1 (95%CI 0.1, 0.1). The trends in incidence and mortality rates are illustrated in table 1 with highest IR noted for black males during the era 2006-2009. The 5-year survival rates for both males (figure 1) and females (figure 2) seem to be trending down over the eras examined. Regression analysis suggests males and other race have increased odds of survival (HR = 0.829, p=0.0078; HR = 0.54 and p=0.0038, respectively).
Conclusions: Similar to myeloma, black patients tend to be diagnosed with SBP younger and have increased incidence. The incidence rates seem to be increasing, highest among blacks males, more likely from increased awareness and diagnosis. The mortality and survival patterns are comparable to whites. Interestingly, while the 5-year survival for myeloma among all racial groups is improving this analysis shows a decreasing trend for SBP. This observation is more likely from including myeloma patients under the diagnosis of SBP over the period of study. Recently, the International Myeloma Working Group (IMWG) clarified the definition of SBP which will help in accurate diagnosis and ultimately can help in accurate representation of the survival trends.
Table 1. Incidence and Mortality Rates across Study Eras (SEER-9), 1973-2009 Years White (IR) White (MR) Black (IR) Black (MR) Other (IR) Other (MR) Male 1973-1980 0 0 0 (0, 0.1) 0 (0, 0.1) 0 (0, 0.2) 0 (0, 0.1) 1981-1985 0 0 0 (0, 0.2) 0 (0, 0.1) 0 (0, 0.2) 0 (0, 0.1) 1986-1990 0.1 (0.1, 0.2) 0.1 (0, 0.1) 0.1 (0, 0.3) 0.1 (0, 0.2) 0.3 (0.1, 0.5) 0 (0, 0.2) 1991-1995 0.2 (0.1, 0.2) 0.1 (0.1, 0.2) 0.2 (0.1, 0.4) 0 (0, 0.1) 0.1 (0, 0.3) 0.1 (0, 0.2) 1996-2000 0.2 (0.2, 0.3) 0.1 (0.1, 0.1) 0.3 (0.1, 0.5) 0.2 (0.1, 0.4) 0.2 (0.1, 0.4) 0.2 (0, 0.4) 2001-2005 0.4 (0.4, 0.5) 0.2 (0.2, 0.3) 0.5 (0.3, 0.7) 0.3 (0.1, 0.6) 0.2 (0, 0.2) 0 (0, 0.2) 2006-2009 0.4 (0.4, 0.5) 0.2 (0.2, 0.3) 0.7 (0.4, 1) 0.3 (0.1, 0.5) 0.1 (0, 0.2) 0.1 (0, 0.2) Female 1973-1980 0 0 0 (0, 0.1) 0 (0, 0.1) 0 (0, 0.1) 0 (0, 0.1) 1981-1985 0 0 0 (0, 0.1) 0 (0, 0.1) 0 (0, 0.1) 0 (0, 0.1) 1986-1990 0.1 (0, 0.1) 0 (0, 0.1) 0.1 (0, 0.2) 0 (0, 0.1) 0 (0, 0.2) 0 (0, 0.2) 1991-1995 0.1 (0.1, 0.1) 0 (0, 0.1) 0.2 (0.1, 0.3) 0.1 (0, 0.2) 0 (0, 0.1) 0 (0, 0.1) 1996-2000 0.1 (0.1, 0.1) 0.1 (0.1, 0.1) 0.1 (0, 0.2) 0.1 (0, 0.2) 0.1 (0.2) 0 (0, 0.1) 2001-2005 0.2 (0.2, 0.2) 0.1 (0.1, 0.2) 0.3 (0.2, 0.4) 0.1 (0, 0.2) 0.1 (0, 0.2) 0 (0, 0.1) 2006-2009 0.2 (0.2, 0.3) 0.1 (0.1, 0.2) 0.3 (0.2, 0.5) 0.2 (0.1, 0.3) 0.1 (0, 0.2) 0 (0, 0.1)
Figure 1. 5-year Survival Rates in males (SEER-9), 1973-2012 Figure 1. 5-year Survival Rates in males (SEER-9), 1973-2012 Figure 2. 5-year Survival Rates in females (SEER-9), 1973-2012 Figure 2. 5-year Survival Rates in females (SEER-9), 1973-2012

Disclosures
Nooka: Spectrum Pharmaceuticals: Consultancy; Onyx Pharmaceuticals: Consultancy.