All of the following statements about Hairy cell leukaemia are true, EXCEPT:
**Core Concept**
Hairy cell leukemia (HCL) is a rare, chronic, and malignant B-cell disorder characterized by the accumulation of abnormal lymphocytes in the bone marrow and peripheral blood. The pathogenesis of HCL involves the clonal proliferation of neoplastic B cells expressing specific surface antigens and having distinctive morphological features, including hair-like projections.
**Why the Correct Answer is Right**
HCL is typically associated with a favorable prognosis and is often treated with purine analogs, such as cladribine or pentostatin, which induce apoptosis in neoplastic B cells. The disease is also associated with the presence of specific surface antigens, including CD103 and CD25, and the absence of CD23. The clinical presentation of HCL can include splenomegaly, cytopenias, and infections due to immunosuppression.
**Why Each Wrong Option is Incorrect**
**Option A:** Hairy cell leukemia is characterized by the presence of hair-like projections on the surface of neoplastic B cells, which is a distinctive feature of the disease. This statement is true.
**Option B:** Hairy cell leukemia is often treated with purine analogs, which are effective in inducing apoptosis in neoplastic B cells. This statement is true.
**Option C:** Hairy cell leukemia is associated with a favorable prognosis, particularly with the advent of effective treatment options. This statement is true.
**Clinical Pearl / High-Yield Fact**
Hairy cell leukemia is a rare disorder, accounting for only 2% of all leukemia cases, and is more common in males than females. The median age at diagnosis is around 50 years, and the disease often presents with splenomegaly and cytopenias.
**Correct Answer: D**