Ngoentra Tantranont M.D.1, Weerapat Owattanapanich M.D.2, Rapeephan Cholkate M.D.1, Tawatchai Pongpruttipan M.D.1 
1Department of Pathologyand 2Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Objective: Primary non-Hodgkin lymphoma (NHL) of the thyroid is a rare tumor. Some studies show association between thyroid lymphomas and concomitant thyroid diseases, mainly lymphocytic thyroiditis. However, this tumor has not been studied in Thailand. .Therefore, herein, we reviewed clinicopathological features of primary thyroid lymphoma including associated thyroid lesions.
Method: All thyroid lymphoma cases diagnosed at Siriraj Hospital during 2006-2013 were reviewed and classifi ed according to the 2008 WHO classifi cation.
Results: There were 36 cases of primary thyroid NHL. Male/female ratio was 1:2.3 with median age of 67.5. Cases included diffuse large B cell lymphoma (DLBCL) (n=16, 44.4%), mucosa-associated lymphoid tissue (MALT) lymphoma (n=7, 19.4%), DLBCL with MALT lymphoma (n=6, 16.7%), occult MALT lymphoma (n=3, 8.3%), DLBCL with grade 3 follicular lymphoma (FL) (n=3, 8.3%) and DLBL with low grade FL (n=1, 2.8%).Among the available cases (n=17), concomitant thyroid diseases were lymphocytic thyroiditis (64.7%), nodular goiter (17.6%), papillary thyroid carcinoma (17.6%) and follicular adenoma (5.9%).Three occult MALT lymphomas were incidentally detected in thyroidectomy specimen from other mass lesions. They ranged from 0.2 to 0.5 cm. All had associated lymphocytic thyroiditis with stage I disease and remained disease-free after thyroidectomy.
Conclusion: Primary thyroid lymphomas occurred mainly in elderly female patients, commonly associated with lymphocytic thyroiditis. DLBCL and MALT lymphomas were the major subtypes. These fi ndings were similar to the previous reports from other regions. In addition, occult MALT lymphoma could be found in conjunction with other thyroid mass. It could possibly be an indolent disease.