DLBCL : Kidney

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Image Description

Most lymphomas in the kidney represent secondary renal involvement. Primary renal lymphomas are rare. Lymphomas arising in the urinary tract and male genital organs make up less than 5% of extranodal lymphomas. Kidney is the most common location for GU lymphomas. The patients are usually middle-aged or older and there is slight male preponderance. Cases have been reported in children, HIV+ve individuals, and immunosuppressed patients. The presenting symptoms include flank pain, palpable mass, renal insufficiency, and hematuria.

Renal lymphomas are bilateral in about 25% of cases. The size ranges from less than 5 cm to massive tumors with complete replacement of renal parenchyma and invasion of adjacent structures such as perinephric fat, psoas muscle, pancreas, or duodenum. Some cases show extension into the renal vein or inferior vena cava. The gross appearance sometimes mimics renal cell carcinoma. The most common type of renal lymphoma is diffuse large B-cell lymphoma (about 40% to 50% of cases).

The nephrectomy specimen shown here is from a 65 y/o male who presented with vague abdominal discomfort and weight loss over a 3 year period. There was a soft, pink-tan, bulging tumor infiltrating the calyceal system and extending into the renal vein. On sectioning, this tumor connected with the nodule on the upper left of the image that is extending into the perinephric tissues. The histologic and immunohistochemical profile (POS: CD20, CD22, kappa light chains; NEG: CD2, CD3, & CD5) were diagnostic of diffuse large B-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.

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