Small lymphocytic lymphoma/Chronic lymphocytic leukemia (SLL/CLL) is the most common lymphoid neoplasm in North America. Prevalence increases with age up to 13% at 65 years.

Clinically presentation is variable. Most patients are asymptomatic; however, some present with co-existing autoimmune hemolytic anemia, infections, lymphadenopathy and hepatosplenomegaly.

It usually involves the blood, bone marrow, lymph nodes, liver, spleen and, infrequently, other sites. SLL/CLL as shown in this case presents histologically with lymph node effacement by a dense lymphocytic infiltrate that is composed of small monomorphic small B-Iymphocytes with round nuclei, clumped chromatin and scant cytoplasm. Lighter paler proliferation centers composed of pro-lymphocytes and para-immunoblasts are characteristic and evident.

Immunohistochemistry analysis demonstrates that the lymphocytes are positive for CD20, CD5, CD23, and BCL-2. They are negative for CD10, cyclin D1 and BCL-6 (not shown). MUM1 labels the cells within the proliferation centers (not shown). CD3 stains a background of small T-Iymphocytes. Ki-67 proliferation index ranges from 2% to up to 10% with a slightly higher proportion of positive cells in the proliferation centers.

Flow cytometry analysis revealed a monoclonal B-cell population, representing approximately 85% of the total leukocyte count, is CD19+, CD20+ (dim/partial), CD5+ (dim), CD10-, CD23+, C038+ (dim/partial) expressing dim lambda light chains.

The course of SLL/CLL is indolent in most patients; however a subset of patients transform to aggressive diffuse large B-cell lymphoma (Richter's syndrome) or classical Hodgkin lymphomas.

This slide shows BCL-2 stain. See related content for H&E, CD20, CD3, CD5, CD23, and cyclin D1 stains.