Clinical Pearls & Morning Reports
Published September 12, 2018
Hairy-cell leukemia is a rare chronic B-cell lymphoproliferative disorder, with only 1000 new cases diagnosed in the United States annually. Read the latest Case Records of the Massachusetts General Hospital here.
Q: Are the hairy cells that give this leukemia its name easily identified on a peripheral-blood smear?
A: Hairy cells are detected on examination of a peripheral-blood smear in approximately 90% of patients who eventually receive a diagnosis of hairy-cell leukemia, but they are often present in small numbers, and an experienced observer may be needed to identify them.
Q: What are some of the features of hairy-cell leukemia?
A: Affected patients are most commonly middle-aged men who seek medical attention when they have symptoms related to massive splenomegaly or cytopenia. Up to 25% of patients with hairy-cell leukemia are asymptomatic at the time of presentation, and the diagnosis is made incidentally. Patients often do not have palpable lymphadenopathy but may present with fatigue, bleeding, or infection due to compromised cell counts.
A: The leukemic cells of hairy-cell leukemia are known to release pathogenic cytokines that cause bone marrow fibrosis and suppression, which are manifested by cytopenia in up to 85% of patients. A dry tap on aspiration, due to reticulin fibrosis in the bone marrow, is a characteristic finding of hairy-cell leukemia and a diagnostic clue. Absolute monocytopenia is a feature often seen in hairy-cell leukemia. Coexpression of CD25 and CD103 is an immunophenotypic pattern that is highly specific to hairy-cell leukemia. The diagnostic armamentarium has taken a great leap forward with the discovery that the BRAF V600E mutation is virtually ubiquitous in patients with hairy-cell leukemia (i.e., present in >97% of patients).
A: Because the disease is indolent, some patients with hairy-cell leukemia can be followed closely without intervention, often for years. If chemotherapy is indicated, the purine analogues cladribine and pentostatin are first-line chemotherapeutic agents; they are associated with complete response rates of up to 75%, overall response rates of up to 95%, and median relapse-free survival of at least 16 years. The two drugs are equally efficacious as well as highly immunosuppressive and myelosuppressive. The percentage of patients who can be cured with current therapies is uncertain, since relapses occur in approximately 50% of patients, both early after the initial treatment (with one quarter occurring within the first 5 years) and even decades later. Retreatment with a course of the same or the alternative purine analogue, often with the addition of rituximab, can induce a second lengthy clinical remission, extending survival over decades.