HCL Meeting 2010
7
Table 1. Immunohistochemical profiles of small B-cell lymphomas which present with splenomegaly and bone marrow disease. CD5 Cyclin D1 Sox11 CD23 CD25 IgD TRAP Annexin A1 CD103 CD11c
Hairy cell Splenic red pulp 77 ND 77 7 7 þþ/77 þ SMZL 77 7
þ 77 þ 7
7 7
7 þþ þ 7
7 7 MCL þþ þ 77 þ 77 7
þ 77 7 þ 77 7
HCL – variant 77 ND 77 7 þ/77 þþ CLL/SLL
7/þ 7/þ
þ
7 7
HCL, hairy cell leukemia; CLL/SLL, chronic lymphocytic leukemia/small lymphocytic lymphoma; SMZL, splenic marginal zone lymphoma; MCL, mantle cell lymphoma; IgD, immunoglobulin D; TRAP, tartrate resistant acid phosphatase; ND, not determined.
resistant acid phosphatase (TRAP) cytochemically to some degree. Although expression of TRAP is not pathognomonic for HCL, bright cytochemical ex- pression of TRAP is almost exclusive to HCL. Histologically, tumor cells are commonly encoun-
Figure 1. Hairy cell leukemia, cytological features. (A) Peripheral blood smear showing characteristic ‘hairy’ cell with cytoplasmic projections and frayed cytoplasmic borders (61000; Wright– Giemsa). (B) Touch preparation from spleen demonstrating representative hairy cells. Note loss of villous cytoplasmic projections (61000; Wright–Giemsa).
The hairy cell expresses isoenzyme 5 of acid
phosphatase. This isoenzyme imparts a resistant to treatment with tartaric acid to the hairy cell and therefore, essentially all cases ofHCL express tartrate
tered within the bone marrow and spleen, and less commonly within the liver and lymph nodes. Bone marrow involvement is variable and displays a broad spectrum of histological appearances, ranging from hypocellular, aplastic-appearing infiltrates to diffuse sheets of monotonous cells replacing marrow ele- ments. The most common pattern observed within the bone marrow is an interstitial infiltrate, which tends to infiltrate throughout the marrow cavity preserving the marrow adipose tissue, rather than a nodular growth pattern [Figure 2(A)]. At low power the infiltrate appears paucicellular and may often be overlooked. The hairy cell’s abundant cytoplasm imparts a well-spaced appearance to the lymphoid cells, as compared to other lymphoid neoplasms. Well-preserved cytoplasmic borders result in a ‘fried egg’ appearance. Hairy cells may disrupt the micro- vasculature of the bone marrow leading to extravasa- tion of red blood cells that may impart a pseudosinus appearance. Similar pseudosinuses and blood lakes are invariably seen in the spleen. Additionally, hairy cells produce and excrete fibronectin which results in pericellular deposition of fibronectin that may also contribute to the widely spaced appearance of the lymphoid cells [2]. It is this pericellular fibronectin that is the most probable cause for the increase in marrow reticulin fibers seen in essentially all HCL cases and is often the culprit of the characteristic ‘dry tap’ observed in this disease. Individual hairy cells can histologically mimic
many common bone marrow elements (monocytes, myelocytes, mast cells, etc.) and, as mentioned previously, when HCL infiltrates interstitially it can be quite inconspicuous. Immunohistochemical ana- lysis is invaluable in highlighting subtle involvement, particularly early in the disease [Figure 2(B)]. CD20 is strongly expressed. Other markers useful in differential diagnosis of the bone marrow core include positive staining for DBA.44, annexin A1,
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