Clinicopathological analysis of primary thyroid non-Hodgkin lymphoma: a single-center study

BACKGROUND: Primary thyroid lymphoma (PTL) is very rare. The aim of this study was to describe the clinical characteristics, pathological features, and survival outcomes of primary thyroid non-Hodgkin lymphoma, including the diagnostic value of clonal immunoglobulin (Ig) gene rearrangements in diagnosing mucosa-associated lymphoid tissue (MALT) lymphoma of the thyroid gland with co-existing Hashimoto thyroiditis (HT). METHODS: Paraffin-embedded tissues of patients diagnosed in our institute with PTL between 2007 and 2021 were collected. Clinicopathological features and follow-up data were retrospectively analyzed. Analysis of clonal Ig gene rearrangements were performed in patients with suspected PTL. RESULTS: Of the 22 patients included in our study, 17 were female. The median age at diagnosis was 65.5 years (range, 44–80 years). We detected 11 cases of diffuse large B-cell lymphoma (DLBCL), 10 cases of MALT lymphoma, and 1 case of T-cell lymphoma. A total of 18 patients (81.8%) had early stage (I/II) disease. B-cell lymphoma showed diffuse positivity for CD20 but negative markers for thyroid-origin cells. Double-hit and triple-hit lymphomas were not found in the 8 DLBCL cases, and 2 cases of HT with lymphoid tissue dysplasia were diagnosed with MALT lymphoma with gene rearrangement testing. The median follow-up time was 47 months (range, 4–160 months), and the overall survival was 80% for MALT lymphoma (8 of 10), 72.7% for DLBCL lymphoma (8 of 11), and 100% for T-cell lymphoma (1 of 1). There was no significant difference between the groups. CONCLUSIONS: PTL mostly affects middle-aged and older adult females with HT, and its main histological type is non-Hodgkin B-cell lymphoma. For patients with HT along with a histologically benign lymphoepithelial lesion, the identification of clonal Ig gene rearrangements is important for differential diagnosis. The prognosis between DLBCL and MALT is not statistically significant.