Real-World Treatment Patterns and Outcomes of Solitary Plasmacytoma in the United States: A National Cancer Database (NCDB) Analysis of Years 2004-2020

Background: Solitary plasmacytoma, whether it affects the bone (P-Bone) or occurs as an extramedullary disease (P-EM), is typically treated with radiation therapy. Surgery, either combined with radiation or as a standalone option, is also recognized as a curative option, especially for P-EM. Prognosis depends on treatment and disease location. In this IRB approved retrospective analysis, the National Cancer Database (NCDB) was utilized to assess treatment patterns and overall survival (OS) among plasmacytoma patients treated at Commission on Cancer (CoC) accredited facilities across the USA.

Methods: N=9,427 plasmacytoma patients from 2004 to 2020 were identified using the NCDB, excluding multiple myeloma patients. Descriptive statistics examined data and differences in primary site, radiation dosage, and treatment patterns. OS tables and Kaplan-Meier curves compared primary sites, radiation dose, and treatment outcomes. Multivariate Cox regression analysis identified independent survival factors. SAS version 9.4 was used to analyze the data.

Results: P-Bone accounted for 73% while P-EM represented 27% of cases. Patients' characteristics are presented in Table 1. The median OS was significantly longer in P-EM patients with OS of 146 months compared to 106 months in P-Bone patients (p<0.0001). Radiation therapy alone was the most utilized modality in both P-Bone (58%) and P-EM (36%), followed by combination of radiation and surgery in 20% and 27% of cases, respectively. Notably, a small proportion of patients received surgery alone (8% in P-Bone and 23% in P-EM). Patients who underwent combined surgery and radiation exhibited the longest median OS of 181 months, compared to 137 months for surgery alone and 116 months for radiation alone (p<0.0001)(Fig 1). Median OS also varied significantly (p<0.0001) based on the radiation dose: <35Gy (46.62 months), 35-39.9Gy (80.66 months), 40-44.9Gy (125.31 months), 45-49.9Gy (151.52 months), and ≥50Gy (176.36 months). Primary P-Bone sites were categorized as follows: limb bones (n=932), skull and mandible (n=571), vertebral column (n=2,729), ribs/sternum/clavicle (n=861), and pelvis (n=991). The median OS varied significantly (p<0.0001) across the bone sites, with the longest median OS of 122.25 months observed in cases involving the skull and mandible (95% CI: 102.34-181.29) followed by vertebral column with OS of 110.88 months (95% CI: 102.87-120.90). Pelvis, ribs/sternum/clavicle, limb bones, and other bones demonstrated median OS values of 108.75 months (95% CI: 88.51-122.71), 105.49 months (95% CI: 88.87-124.42), 96.43 months (95% CI: 79.61-122.68), and 72.18 (95% CI: 60.65-93.01) respectively (p<0.0001). In most bone sites, the predominant radiation dose fell within the range of 45-49.9 Gy (21.67% for limb bones, 26.78% for skull and mandible, 32.28% for vertebral column). However, the ribs/sternum/clavicle and pelvis categories stood out, with the predominant radiation dose being equal to or exceeding 50 Gy (32.96% for ribs/sternum/clavicle, 29.9% for pelvis). Furthermore, radiation therapy alone emerged as the predominant treatment modality across all bone sites.

Conclusion: This 16-year study to 2020 is the largest database to date in the USA that analyzes the real-world treatment patterns and OS of P-bone and P-EM. Long term median survival of greater than 9 years was observed for solitary plasmacytoma. Combined surgery and radiation therapy showed improved survival outcomes in solitary plasmacytoma, emphasizing the role for combined modality in selected sites, but optimal radiation dose is unclear. P-Bone, given the locations, are generally treated with radiation only. Therefore, evaluation of the radiation dose for curative modality is pertinent for management. This study suggests 45-50 Gy may confer better survival than lower dosage. Guidelines for radiation dose vary. Our study provides an additional 7-year data to a published database to 2013 (Ghiassi-Nejad et al.) with similar OS. We further stratified the outcome of P-bone, the bulk of solitary plasmacytoma by site of disease and radiation dose along with patient characteristics. Although higher doses have benefit for survival, modern techniques will hopefully decrease comorbidities that can occur locally and longitudinally. Our large dataset can provide reference to develop better guidelines for management of solitary plasmacytoma, especially P-bone.