Primary Thyroid Lymphoma: An Analysis of the National Cancer Database

Background

Primary Thyroid Lymphoma (PTL) is a rare malignancy, representing only 1-5% of thyroid malignancies and 2.5-7% of all extra nodal lymphomas. Most cases of PTL are of B-cell origin, and 98% of all PTL is 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. Due to limited studies the optimal treatment of PTL has not yet been established. Using the National Cancer Database (NDCB) we aimed to evaluate patient characteristics, treatment modalities, and overall survival. This is the first NCDB study completed on PTL, and the only large retrospective study to examine the use of chemotherapy and immunotherapy in treatment of these patients.

Methods

The NCDB for Non-Hodgkin lymphoma was utilized to identify 3466 patients diagnosed with PTL between 2004-2015. 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

Median overall survival was 11.6 years (95% Confidence Interval (CI) 11.1 - 12.1 years), with a 59% 5-year overall survival and 49% 10-year overall survival. 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, 18.3% marginal zone lymphoma, 8% follicular lymphoma, and 1.9% Burkitt lymphoma. Regarding treatment, 57.6% of patients received no radiation and 40.6% received beam radiation. 54% received some form of surgical treatment. Single agent chemotherapy was used in 3.5% of patients, 60.7% received multiagent chemotherapy and 29.9% of patients received no chemotherapy. Immunotherapy was used in 11.1% of patients.

On multivariate analysis, increased risk of death was significantly associated with increasing age, race other than white, and higher disease stage. Hazard ratios for treatment modalities were found to be 0.684 with beam radiation (p<.001), 0.58 for surgical treatment (p<.001), 0.63 for chemotherapy (p<.001), and 1.082 for immunotherapy (p=.560). Other factors associated with decreased risk of death include treatment at academic centers (HR 0.846, p<.05) and integrated cancer centers (HR 0.76 p<.05) when compared to community centers.

Conclusion

This is the largest study to date to describe patient characteristics, treatment modalities, and overall survival in PTL and to compare treatment options with overall survival. Beam radiation, chemotherapy, and surgical resection all reveal significant survival benefit, where immunotherapy is not associated with a significantly reduced risk of death.