MON-441 Primary Thyroid Maltoma: A Rare Non-hodgkin Malignancy

Introduction: Thyroid lymphoma is a rare malignancy; only 2% of extranodal lymphomas arise within the thyroid gland. Furthermore, lymphomas represent no more than 2% of all malignant thyroid tumors and almost always non-Hodgkin type. Case: A 58-year-old female with a medical history of rheumatoid arthritis treated with Golimumab for years. Exam revealed a right thyroid lobe enlargement with bilateral palpable nodules. Labs include TSH of 1.4 mU/L, Free T4 of 1.76 ng/dL, normal anti-thyroid peroxidase antibodies, but elevated anti-thyroglobulin. US of the thyroid showed right-sided, hyperechoic nodule measuring 1.3cm, and left-sided solid hypoechoic nodule measuring 2.2cm. US-guided FNA of the right nodule yielded atypical cells of undetermined significance (2017 Bethesda category III). FNA of the left nodule showed severe, chronic thyroiditis, with small clonal population of cells and suspicion for lymphoma. She underwent total thyroidectomy with left central lymph node dissection. Microscopic evaluation showed a predominant lymphocytic population with plasmacytoid/plasma cells. The histological finding was consistent with extranodal marginal zone lymphoma (EMZL) of mucosa-associated lymphoid tissue (MALT lymphoma or MALToma). However, thyroid tissues were negative for clonal immunoglobulin gene rearrangements (both immunoglobulin heavy and light chains). Immunohistochemistry demonstrated that the tumor cells were CD19, CD 20, CD 22, PAX5, CD78A positive, highlighting predominantly small to medium-sized B- cell lymphocytes, along with plasmacytoid/plasma cells (MUM1 and CD 75A positive). Furthermore, occasional reactive germinal centers (CD10, BCL6 positive, BCL2 negative) were noted. In conclusion, these features were consistent with a low grade, non-Hodgkin’s lymphoma of MALT type. Discussion: EMZL is a clinically indolent non-Hodgkin lymphoma, and growing evidence suggests that numerous cases originate in the background of chronic immune stimulation. MALToma is associated with Hashimoto’s thyroiditis or other immune diseases. Whereas half of EMZL can still arise without a Hashimoto thyroiditis background. Characteristics of the MALToma include reactive follicles, with the neoplastic cells invading the marginal zone (small lymphocytes, marginal zone B-cells, and plasma cells). The key findings are the presence of clonality (light chain restriction), and confirmation of B-cell origin (presence of B-cell markers). The immunophenotype is confirmed by immunohistochemistry and flow cytometry. Localized EMZL of the thyroid can be effectively treated with radiation alone. Surgery is usually used for diagnostic biopsy only. Chemotherapy is usually reserved for those with advanced stages