Hairy Cell Leukemia
Hairy cell leukemia is a malignancy of
uncertain classification, predominantly affecting elderly males. The clinical
presentation is nonspecific, and includes malaise, fatigue, and frequent
infectious episodes. The physical examination usually shows splenomegaly and
sometimes generalized lymphadenopathy. The diagnosis is based on the finding of
atypi-cal lymphocytes with numerous finger-like (or hairy) projections in the
peripheral blood defining the disease (which derives its name from the
morphological characteristics of the abnormal lymphocytes). The abnormal cells
have mixed characteristics. On the one hand they express membrane
immunoglobulins, often of several isotypes, and synthesize mono-typic heavy and
light chains, suggesting a B-lymphocyte origin. However, after mitogenic
stimulation, the abnormal lymphocytes may express the CD2 and CD3 membrane
markers characteristic of T lymphocytes. On the other hand, they have
monocyte/macrophage func-tions and markers including phagocytic properties, the
ability to produce and release lysozyme and peroxidase, and the presence of
intracellular tartrate-resistant acid phos-phatase. These findings have been
interpreted as indicating the proliferation of B-cell pre-cursor cells sharing
monocytic and T-cell markers and functions, malignant chimeric cells with
multiple lineages, or malignant lymphocytes with aberrant gene expression.
Without additional data it is impossible to decide which of these possibilities
is more likely to re-flect accurately the nature of the malignant proliferation
in this type of leukemia.
Interferon-α is
therapeutically useful (sometimes inducing permanent remissions) in hairy cell
leukemia. This seems to result from a direct antiproliferative effect that is
at-tributed to the ability of interferon-α to
promote redifferentiation of malignant cells, stop-ping their uncontrolled
multiplication.
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