DLBCL : Thyroid

Image 89 of 89

Image Description

Diffuse Large B-cell Lymphoma of Thyroid: Primary lymphomas of the thyroid account for 1% to 5% of all thyroid malignancies and comprise 1% to 2.5% of all lymphomas. They are usually seen in older individuals (median age 60-70 years) with a female predominance.

In most patients, thyroid lymphomas arise in a background of Hashimoto thyroiditis (which causes 40-80 fold increased risk for thyroid lymphomas as compared to individuals without Hashimoto thyroiditis). Patients usually present with a rapidly enlarging neck mass which may be accompanied by cough, dyspnea, hoarseness, and dysphagia.

Macroscopically, thyroid lymphomas may be multinodular (as shown in this image) or produce diffuse enlargement of a lobe or entire gland. They may be soft or firm with smooth pink-tan or greyish-white appearance. Morphologically, the most common subtype of thyroid lymphoma is diffuse large B-cell lymphoma (DLBCL) accounting for 60-90% of cases. The second most common subtype is MALT lymphoma (10-30% of cases). Many of the DLBCL cases arise by transformation of underlying MALT lymphoma. Less than 10% of cases consist of follicular lymphomas, Burkitt lymphoma, and peripheral T-cell lymphoma.

About the Disease

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma accounting for about 30% of all cases. It is an aggressive malignancy and is seen mostly in adults (median age 64 years). Patients present with rapidly enlarging lymph nodes or tumor masses (extranodal sites). Extranodal sites are commonly involved (almost 40% of cases) and include gastrointestinal tract, central nervous system, skin, mediastinum, and bone, but any organ can be involved. Bone marrow and liver involvement is less frequent than in follicular lymphoma or small lymphocytic lymphoma. Morphology: The cut surface of involved lymph nodes or tissues is soft and fleshy with effacement of the native architecture. There is diffuse proliferation of large to medium-sized lymphoid cells which can be classified into following subtypes: 1) Centroblasts - round, angular, or multilobated vesicular nuclei; multiple small peripheral nucleoli; indistinct amphophilic cytoplasm. 2) Immunoblasts - round or oval vesicular nuclei; single prominent central nucleolus; abundant basophilic cytoplasm. 3) Anaplastic - markedly pleomorphic large tumor cells. Necrosis, numerous mitoses, and starry sky pattern may also be seen. Immunophenotype: DLBCL expresses CD45 and pan B-cell markers such as CD20, CD22, CD79a, and PAX-5. Monotypic immunoglobulin (surface or cytoplasmic) is variably present. Other positive markers include CD10 (40% cases), BCL6 (60% cases), and BCL2 (50% cases). CD5 is present in about 10% of cases. A small number of cases show post-germinal center or plasma cell-associated markers such as CD38, VS38, and MUM1. Ki-67 labeling index is high (>20%). A minority of cases express CD30. Pan-T markers are negative. Molecular genetics: Immunoglobulin heavy- and light-chain genes are rearranged. The immunoglobulin heavy-chain variable region gene is hypermutated. Rearrangements of BCL2 and BCL6 genes are seen in 20% and 30% of cases respectively. MYC (8q24) translocation is seen in about 10% of cases, usually fused to a non-immunoglobulin gene in contrast to Burkitt lymphoma.

Image 89 of 89