* The coexpression of CD5 and CD10 has previously been reported in cases of intermediate- and high-grade lymphomas and in precursor B cells in normal or regenerating bone marrow. We report 3 cases of low-grade B-cell lymphoma that were found to coexpress CD5 and CD10 at the time of initial diagnosis. The first case was classified as small lymphocytic lymphoma; the second as follicle center lymphoma, follicular grade 1; and the third as small B-cell lymphoma otherwise not specified. Currently, the clinical implication of the coexpression of CD5 and CD10 is not known. We describe this finding to highlight the difficulty that may be encountered in classifying lymphomas in cases where this coexpression is present.

Immunophenotyping by immunohistochemical studies and flow cytometry is routinely used in the diagnosis of low-grade lymphomas. Small lymphocytic and mantle cell lymphomas are typically positive for CD5 and negative for CD10,1 follicle center cell lymphomas are usually CD10 positive and CD5 negative,’ and marginal zone lymphomas are usually negative for CD5 and CD10.2 We report 3 cases of small B-cell lymphoma with different morphologic features (1 small lymphocytic, 1 follicle center, and 1 unclassifiable), all of which coexpress CD5 and CD10. The third case in particular highlights the difficulty that may be encountered in classifying lymphomas when unusual coexpression is found.

A 69-year-old woman was evaluated for a “cyst” in the right subclavian region. A mass was excised and a diagnosis of small lymphocytic lymphoma was made. Grossly, the specimen consisted of an encapsulated soft tissue mass measuring 2 cm in greatest dimension. The cut surface was yellow and resembled a lipoma. Microscopically, the lymph node architecture was partially effaced by an interfollicular proliferation of round lymphoid cells with scattered prolymphocytes . By immunohistochemical stains, the cells were immunoreactive for CD20, CD23, BCL-2, and both CD5 and CD10. BCL-1 and CD3 were negative. No additional material was received by the pathologist for staging, and no clinical follow-up is available.

Case 2

The second patient, an 88-year-old, white woman, presented with a scalp lesion. The lesion was excised, and a diagnosis of follicle center cell lymphoma, grade 1, was made. No peripheral lymphadenopathy was present. Grossly, there was a 4-cm skin ellipse with an attached 3-cm, ill-defined nodule. Microscopically, the tumor cells were in a follicular pattern involving both superficial and deep dermis. The follicles were composed of predominantly small cleaved cells. By immunohistochemical stain, the cells were immunoreactive for CD20, BCL-2, and both CD5 and CD10 . BCL-1 and CD3 were negative.

The pathologist received no additional material. By physical examination, there was no evidence of adenopathy, and computed tomographic scans of the chest, abdomen, and pelvis were negative. The patient received a course of radiation without complication, with last known follow-up 5 months after the scalp excision.

Case 3

The third patient, an 81-year-old man, presented with pancytopenia and splenomegaly. A bone marrow biopsy was performed, and a diagnosis of a B-cell low-grade lymphoproliferative disorder was made. Examination of peripheral blood revealed a relative but not absolute lymphocytosis. The lymphocytes were somewhat irregular without prominent projections. The bone marrow biopsy specimen was normocellular with multiple nonparatrabecular lymphoid aggregates comprising 10% of the cellularity.