HCL Meeting 2010 HCL-v cases share some features with classic HCL
but show differences in hematologic, cytologic, and immunophenotypic features, and lack responsiveness to classic HCL therapies [6]. Some hematologic variances include leukocytosis and the presence of monocytes. Cytologic variances include the presence of prominent nucleoli, resembling prolymphocytes. As mentioned earlier, HCL-v, even with all its similarities to HCL, should be thought of as a completely separate disease and treated as such. Within the spleen, HCL-v maintains the pure red pulp distribution of HCL and can similarly form blood lakes. Bone marrow involvement by HCL-v is also similar to HCL; however, unlike HCL the bone marrow is aspirable and without significant reticulin fibrosis. Additionally, the degree of peripheral blood involvement is usually greater. HCL-v cells variably express TRAP; CD25, cyclin D1, and annexin A1 are characteristically absent, although CD103may be expressed. SMZL is characterized by loosely organized nod-
ular, non-paratrabecular, lymphoid infiltrates in the bone marrow, rather than the interstitial pattern of HCL. The lymphoid cells have a moderate amount of pale cytoplasm, with indistinct cytoplasmic borders. Some cases may show an intrasinusoidal distribution of tumor cells. As in HCL, there may be marked splenomegaly without peripheral lymphadenopathy. The pattern of involvement in the spleen is starkly different from that ofHCL, with predominantly white pulp, rather than mainly red pulp involvement. Splenic diffuse red pulp small B-cell lymphoma is
included as a provisional entity in the 2008 WHO classification. It appears to correspond to many cases previously diagnosed as SLVL [7,8]. A typical feature is an intrasinusoidal localization pattern in the bone marrow (Figure 4). Peripheral blood involvement is generally more prominent than seen in HCL, especially early in the course of the disease. The cells have abundant pale cytoplasm, often with villous projections mimicking hairy cells. As the name implies, in the spleen the neoplastic cells diffusely infiltrate the red pulp, involving both cords and sinuses. Blood lakes are usually absent. Im- munophenotypic studies are useful in the distinction with HCL, as the cells express B-lineage markers, but annexin A1 is consistently negative; the cells usually lack immunoglobulin D (IgD), CD5, CD25, CD103, and CD11c. HCL is a characteristic entity that demonstrates a
significant response to disease appropriate therapy. An appropriate diagnosis can be rendered in nearly all situations due to the reliable and reproducible cytomorphologic and immunophenotypic features of this disease. Morphologically similar lymphoproli- ferative disorders differ in their response to HCL
9
Figure 4. Differential diagnosis of hairy cell leukemia. (A) Peripheral blood with features of splenic lymphoma with villous lymphocytes (SLVL). This pattern is most commonly associated with diffuse red pulp small B-cell lymphoma. The cells have ample cytoplasm and villous cytoplasmic projections morphologically consistent with ‘hairy’ cells (6400; Wright–Giemsa). (B) CD20 immunohistochemical stain highlights the typical intrasinusoidal localization of the neoplastic cells (640; IHC).
therapy, and therefore careful diagnostic evaluation is essential.
Potential conflict of interest: Disclosure forms provided by the authors are available with the full text of this article at
www.informahealthcare.com/ lal.
References
1. Swerdlow SH, Campo E, Harris NL, et al. WHO classification of tumours of haematopoietic and lymphoid tissues. 4th ed. Lyon, France: IARC; 2008.
2. Burthem J, Cawley JC. The bone marrow fibrosis of hairy- cell leukemia is caused by the synthesis and assembly of a fibronectin matrix by the hairy cells. Blood 1994;83:497– 504.
3. Falini B, Tiacci E, Liso A, et al. Simple diagnostic assay for hairy cell leukaemia by immunocytochemical detection of annexin A1 (ANXA1). Lancet 2004;363:1869–1870.
4. Chen YH, Gao J, Fan G, Peterson LC. Nuclear expression of sox11 is highly associated with mantle cell lymphoma but is independent of t(11;14)(q13;q32) in non-mantle cell B-cell neoplasms. Mod Pathol 2010;23:105–112.
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