Abstract
Hairy cell leukemia/lymphoma (HCL) is a rare B-cell neoplasm primarily involving spleen, bone marrow, and blood. However, other sites of primary involvement do occur and can present a diagnostic and therapeutic challenge. We present an unusual case of HCL involving predominantly the breast that was diagnosed as an incidental finding during an elective reduction mammoplasty in an otherwise healthy asymptomatic woman. Bone marrow performed for staging revealed limited involvement by HCL. Notably, there was no splenomegaly and/or involvement of other extramedullary sites. The peripheral blood revealed minimal involvement detected by flow cytometry. Extensive immunohistochemical studies supported by positive BRAF V600E mutational status confirmed the diagnosis of HCL. The patient remains asymptomatic without treatment one year following the diagnosis. This is the first case of a well-documented HCL presenting primarily in the breast in an asymptomatic patient. We review the literature on extramedullary, extrasplenic involvement by HCL and discuss the diagnostic challenges as well as the utility of immunohistochemistry and molecular studies in the diagnosis of atypical presentations of HCL.
Highlights
Hairy cell leukemia (HCL) was first identified as a distinct clinical and histopathologic entity by Bouroncle et al in 1958
HCL is recognized as a neoplasm of mature B-cell involving blood, bone marrow, and splenic red pulp
Immunohistochemical staining revealed that the infiltrating lymphocytes were CD20 and PAX5 positive B-cells showing variable nuclear expression of Cyclin D1 as well as cytoplasmic Annexin-A1 and TRAP (Figures 1(d)–1(f)) and weak CD25
Summary
Hairy cell leukemia (HCL) was first identified as a distinct clinical and histopathologic entity by Bouroncle et al in 1958. He described an indolent disorder and characterized its clinical course, pathologic features, treatment options, and prognosis [1, 2]. HCL is recognized as a neoplasm of mature B-cell involving blood, bone marrow, and splenic red pulp. HCL affects adults with median age of 50 years and shows a male to female predominance of 4 : 1; it usually has an indolent, chronic course characterized by progressive pancytopenia, splenomegaly, and frequently monocytopenia. Circulating small monocytoid B-cells “hairy cells” with the characteristic hair like cytoplasmic projections are generally rare and can be difficult to identify on the peripheral blood smear [4]
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