Primary Thyroid Lymphoma: An Analysis of the National Cancer Database.

Introduction Primary thyroid lymphoma (PTL) is a rare malignancy, representing only 1% to 5% of thyroid malignancies and 2.5% to 7% of all extranodal lymphomas. Most cases of PTL are of B-cell origin, and 98% of all PTL cases are non-Hodgkin's lymphoma. Case series and case reports represent the majority of the available studies on PTL, with a paucity of large retrospective population studies available for this disease. This is the first National Cancer Database (NCDB) study completed on PTL and the only large retrospective study to examine the use of chemotherapy and immunotherapy in the treatment of this specific population. Methods The NCDB for non-Hodgkin's lymphoma was utilized to identify 3,466 patients diagnosed with PTL between 2004 and 2015. The database was used to examine demographic information including age, race, gender, histology, stage, and treatment modality. Bivariate Kaplan-Meier analysis with log-rank tests was used to analyze overall survival. Multivariate analysis was performed with Cox proportional hazards regression models to obtain hazard ratios to assess the association of patient characteristics and treatment methods with survival. Results The median all-cause survival for PTL was 11.6 years (95% confidence interval [CI]: 11.1 to 12.1 years). The majority of PTL patients were female (68%) and white (93%), with a mean age of 65.8 years. Histologically, 59.5% of cases were diffuse large B-cell lymphoma (DLBCL), 18.3% marginal zone lymphoma, 8% follicular lymphoma, and 1.9% Burkitt lymphoma. Regarding treatment, 40.6% received beam radiation, and 54% underwent surgical resection. Single-agent chemotherapy was used in only 3.5% of patients, where 60.7% received multiagent chemotherapy. Additionally, immunotherapy was used in 16.2% of patients. There was a significantly increased risk of mortality associated with increasing age, DLBCL histology, and higher disease stage. Multivariate analysis of treatment methods revealed that lobectomy (hazard ratio [HR]: 0.58, 95% CI: 0.47-0.73) and total or subtotal thyroidectomy (HR: 0.58, 95% CI: 0.47-0.71) had significantly improved survival rates over no surgical management (< 0.001). Beam radiation (HR 0.67, 95% CI: 0.58-0.79) had a significant survival benefit over treatment regimens that did not include radiation therapy (< 0.001). Multiagent (HR: 0.40, 95% CI: 0.33-0.49) and single-agent chemotherapy (HR: 0.43, 95% CI: 0.30-0.63) had significant improvement over treatment regimens that did not include chemotherapy (< 0.001). Immunotherapy had a survival benefit (HR 0.87) although this was not found to be statistically significant (95% CI: 0.68-1.11). Other factors associated with decreased risk of mortality include treatment at academic medical centers (HR: 0.846) and integrated cancer centers (HR: 0.76) as compared to community centers (< 0.05). Conclusion This is the largest study to date of PTL and the first to analyze the NCDB database. Patient characteristics, treatment modalities, and overall survival in PTL were examined to further characterize this rare disease. Beam radiation, chemotherapy, and surgical resection all reveal significant survival benefit, with multiagent chemotherapy having the greatest advantage.