Farming and gardening correlate with an increased risk of HCL development in some studies which does not necessarily imply causation.A 2011 study identified somatic BRAF V600E mutations in all 47 HCL patients studied, and no such mutations in the 193 peripheral B-cell lymphomas/leukemias other than HCL.The U.S. Institute of Medicine (IOM) found a correlation which permits an association between exposure to herbicides and later development of chronic B-cell leukemias and lymphomas in general. The IOM report emphasizes that neither animal nor human studies indicate an association of herbicides with HCL specifically. However, the IOM extrapolated data from chronic lymphocytic leukemia and non-Hodgkin lymphoma to conclude that HCL and other rare B-cell neoplasms may share this risk factor. As a result of the IOM report, the U.S. Department of Veterans Affairs considers HCL an illness presumed to be a service-related disabilityHuman T-lymphotropic virus 2 (HTLV-2) has been isolated in a small number of patients with the variant form of HCL. In the 1980s, HTLV-2 was identified in a patient with a T-cell lymphoproliferative disease; this patient later developed HCL, but HTLV-2 was not found in the hairy cell clones. There is no evidence that HTLV-II causes any sort of hematological malignancy, including HCL. Pathophysiology
Pancytopenia in HCL is caused primarily by marrow failure and splenomegaly. Bone-marrow failure is caused by the accumulation of hairy cells and reticulin fibrosis in the bone marrow, as well as by the detrimental effects of dysregulated cytokine production.
In all patients, the first two years after diagnosis have the highest risk for fatal outcome; generally, surviving five years predicts good control of the disease. After five years clinical remission, patients in the United States with normal blood counts can often qualify for private life insurance with some US companies.Accurately measuring survival for patients with the variant form of the disease (HCL-V) is complicated by the relatively high median age (70 years old) at diagnosis. However, HCL-V patients routinely survive for more than 10 years, and younger patients can likely expect a long life. Follow-up care
Despite decade-long remissions and years of living very normal lives after treatment, hairy cell leukemia is officially considered an incurable disease. While survivors of solid tumors are commonly declared to be permanently cured after two, three, or five years, people who have hairy cell leukemia are never considered cured. Relapses of HCL have happened even after more than twenty years of continuous remission. Patients will require lifelong monitoring and should be aware that the disease can recur even after decades of good health. While most oncologists consider Hairy Cell Leukemia to be incurable, there is some evidence that some patients are in fact cured after treatments. Of the original 358-patient cohort treated with cladribine at the Scripps Clinic, 9 of 19 in continuous CR for a median of 16 years were free of HCL MRD by flow cytometry and IHC.