Case of the Month: Spleen

This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2014, case 18 and is a splenic marginal zone lymphoma.

The diagnosis is splenic marginal zone lymphoma (SMZL). Sections of spleen show involvement of both the red and white pulp by this B-cell neoplasm. The white pulp is markedly expanded and nodular with prominent, pale marginal zones comprised of small-medium sized lymphocytes with scattered large transformed cells. Focally, the pale marginal zones surround central areas of the white pulp that are dark, composed of small lymphocytes. The red pulp contains small nodules to sheet-like proliferations of neoplastic, pale, small-medium lymphocytes.

SMZL is often indolent, presenting in adults with symptoms that are associated with splenomegaly, such as anemia, thrombocytopenia and less frequently left upper abdominal pain and sense of satiety without eating. Usually, no lymphadenopathy is present. Occasionally, SMZL is associated with a small monoclonal protein without hypergammaglobulinemia or hyperviscosity and has been noted to be associated with hepatitis C in southern Europe. Regarding treatment of this indolent neoplasm, SMZL responds to splenectomy as well as to chemotherapy. Even with bone marrow involvement, the prognosis of SMZL is good. Rarely, transformation to large B-cell lymphoma may occur. If SMZL is associated with hepatitis C, interferon gamma antiviral treatment is effective.

SMZL shows infiltration by the neoplastic lymphocytes in the splenic red and white pulp. The typical germinal center appearance of the white pulp is effaced by marked expansion of the marginal zone. The marginal zone is composed of pale, large lymphocytes with dispersed chromatin and abundant pale cytoplasm. The expanded marginal zone surrounds a central area of small, round lymphocytes that give a dark appearance to the central area of the follicle at low power. The red pulp contains scattered nodules of the large, pale cells and sheets of small, round lymphocytes. Plasmacytic differentiation may occur and clusters of plasma cells may be found in the centers of the white pulp nodules. The splenic hilar lymph nodes are often involved, often lacking a distinct marginal zone due to mixture of small lymphocytes and larger marginal cells. However peripheral lymphadenopathy and extra-nodal involvements are absent. The liver is involved in 30% cases. Bone marrow involvement, present in 80% cases, shows multiple patterns including interstitial, diffuse, and most commonly, nodular infiltrates that may be paratrabecular. Benign germinal centers may also be present. Bone marrow sinusoidal infiltration is characteristic of SMZL, although this finding is non-specific. Peripheral blood smears may show circulating lymphoma cells, termed villous lymphocytes that are small to medium in size with condensed chromatin, inconspicuous nucleoli and scant to moderate cytoplasm. Characteristically, the cytoplasm contains short cytoplasmic projections that are often located to one side of the cell (i.e., polar projections), in contrast to the circumferential projections of hairy cell leukemia cells.

The B-cell origin of SMZL is highlighted by immunophenotypic analysis, as the neoplastic B-cells are positive for CD19, CD20, CD79a and monoclonal surface immunoglobulin, usually IgM. SMZL is negative for CD5 and CD10. Genetic studies may reveal deletion of 7q31-32 or trisomy 3.

Hairy cell leukemia morphologically appears as diffuse infiltration of the red pulp in contrast to red and nodular white pulp involvement observed in SMZL. In addition, immunohistochemical studies of hairy cell leukemia show CD103 and annexin A1 positivity. Notably, SMZL cells are occasionally positive for DBA.44, CD11c, and CD103, the typical markers of hairy cell leukemia. In addition, hairy cell leukemia can show weak positivity of cyclin D1. This pattern of weak expression is in contrast to mantle cell lymphoma which shows strong nuclear cyclin D1 expression. SMZL does not show cyclin D1 expression by immunohistochemical studies.

Chronic lymphocytic leukemia/Small lymphocytic lymphoma (CLL/SLL) also affects the splenic red and white pulp, however the SMZL pattern of nodular expansion of white pulp with spilling of neoplastic cells into the red pulp is not present in CLL/SLL. Mantle cell lymphoma shows atrophic germinal centers with obliteration of splenic germinal centers and follicular lymphoma shows true follicular nodularity. Immunophenotypic analysis may be used to exclude mantle cell lymphoma, CLL/SLL and follicular lymphoma. Mantle cell lymphoma is positive for CD5 and cyclin D1 and CLL/SLL is positive for CD5 and CD23. Similar to SMZL, follicular lymphoma is CD5 negative, however unlike SMZL, follicular lymphoma is CD10 positive and BCL6 positive.

Both T-cell large granular lymphocytic leukemia and hepatosplenic T-cell lymphoma may present with splenomegaly. T-cell large granular lymphocytic leukemia commonly has associated hypergammaglobulinemia and peripheral blood lymphocytosis, with circulating lymphocytes containing prominent azurophilic granules in abundant cytoplasm. This is an indolent T-cell neoplasm. In contrast, hepatosplenic T-cell lymphoma is an aggressive disease with a median 3 year survival. This lymphoma typically presents in young adults, predominantly males. Hepatosplenic T-cell lymphoma frequently shows infiltration of the liver and spleen sinuses by the neoplastic T cells, and sometimes bone marrow sinuses. Both T-cell large granular lymphocytic leukemia and hepatosplenic T-cell lymphoma are T-cell in origin and would quickly be excluded with CD20 immunohistochemistry study.

1. A 65-year-old woman presents with splenomegaly and pancytopenia. Peripheral blood shows lymphocytes with indented nuclei and cytoplasmic projections. The spleen shows diffuse infiltration of the red pulp by neoplastic cells. Immunohistochemical studies are positive for CD19, CD20 and CD79a, CD25 and annexin A1 and weakly cyclin D1. Which of the following is the most likely diagnosis?
   
   1. Diffuse large B-cell lymphoma
   2. Follicular lymphoma
   3. Hairy cell leukemia
   4. Mantle cell lymphoma
   5. Splenic marginal zone lymphoma
2. Which of the following is true regarding splenic marginal zone lymphoma?
   
   1. Deletion 7q is diagnostic of splenic marginal zone lymphoma.
   2. Hepatitis C virus can be associated with splenic marginal zone lymphoma and may be treated with interferon gamma antiviral therapy.
   3. Splenic marginal zone lymphoma peripheral blood lymphocytes are indistinguishable from those of hairy cell leukemia.
   4. Splenic marginal zone lymphoma has an aggressive course and splenectomy is contraindicated.
   5. Splenic marginal zone lymphoma often involves peripheral lymph nodes.
3. Which of the following immunohistochemical studies may be positive in splenic marginal zone lymphoma?
   
   1. Annexin A1
   2. CD10
   3. CD103
   4. CD5
   5. Cyclin D1

1. Kansal R, Ross CW, Singleton TP, et al. Histopathologic features of splenic small B-cell lymphomas. A study of 42 cases with a definitive diagnosis by the World Health Organization classification. Am J Clin Pathol. 2003;120(3):335-347.
2. Kjeldsberg CR, Perkins SL. Practical Diagnosis of Hematologic Disorders. Chicago, IL: ASCP Press; 2010.
3. Kurtin PJ. Indolent lymphomas of mature B lymphocytes. Hematol Oncol Clin North Am. 2009;23(4):769-790.
4. Swerdlow SH, Campo E, Harris NL, et al. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, FR: The International Agency for Research on Cancer (IARC); 2008.

2014
Nichole Steidler, MD FCAP
Surgical Pathology Committee
Hematopathology Fellow
University of New Mexico
Albuquerque, NM

1. Hairy cell leukemia (c). 
2. Hepatitis C virus can be associated with splenic marginal zone lymphoma and may be treated with interferon gamma antiviral therapy (b). 
3. CD103 (c).