Epidemiology and Survival of Primary Extraosseous Plasmacytoma: Insights from A Population-Based Study with A 20-Year Follow-Up

Background Primary extraosseous plasmacytoma (PEP) is a rare and localized form of plasmacytoma that is not well understood. This study aimed to investigate the clinical features and prognostic factors associated with PEP. Methods Using the Surveillance, Epidemiology, and End Results (SEER) database, patients diagnosed with PEP between 2000 and 2019 were extracted. Survival curves were calculated with the Kaplan-Meier method, and prognostic factors were identified based on the univariate and multivariate Cox regression analyses. A nomogram was constructed to predict survival at 3 and 5 years after diagnosis. Results A total of 1044 PEP patients were included in this study. The average age was 60.3 ± 15.2 years, with 64.3% being male (male: female = 1.8:1) and 53.8% being over 60 years old. The most affected sites were the upper aerodigestive tract (42.6%). Most patients received radiotherapy (60.7%), followed by surgery (52.8%) and chemotherapy (15.1%). Overall survival (OS) rates were 88.3% at 1 year, 78.1% at 3 years, 70.7% at 5 years, and 56.0% at 10 years. Corresponding cancer-specific survival (CSS) rates were 92.1%, 85.8%, 82.5%, and 78.1%, respectively. Multivariate cox analysis indicated that age, race, marital status at diagnosis, radiotherapy, chemotherapy, and surgery were independent prognostic factors for OS, while age, race, radiotherapy, chemotherapy, and surgery were independent prognostic factors for CSS. Nomograms were further constructed to predict the possibility of OS and CSS with good performances. Conclusions The survival outcome of patients with PEP depends on several factors including age, race, marital status, and treatment options such as chemotherapy, radiotherapy, and surgery, which were also identified as independent predictors of OS for PEP. Patients who were younger, Asian or Pacific Islander, American Indian or Native American, and received radiotherapy or surgery had a more favorable prognosis, while those who underwent chemotherapy had poorer outcomes. This study provides valuable insights into the management of PEP.