**Question:** Treatment of choice for hairy cell leukaemia is

A. Rituximab
B. Chemotherapy
C. Radiotherapy
D. Bone marrow transplantation

**Correct Answer: A. Rituximab**

**Core Concept:**
Hairy cell leukemia (HCL) is a rare type of lymphoproliferative disorder characterized by the abnormal proliferation of hairy cells in the bone marrow, spleen, and lymph nodes. Hairy cells are B-cells with unique, filopodia-like projections on their surface. Rituximab is a monoclonal antibody targeting the CD20 antigen found on the surface of mature B-cells, including hairy cells.

**Why the Correct Answer is Right:**
Rituximab is a monoclonal antibody that binds to the CD20 antigen on the surface of hairy cells, leading to their destruction by the immune system. By targeting hairy cells specifically, Rituximab minimizes the damage to normal B-cells, reducing the risk of secondary effects associated with chemotherapy and bone marrow transplantation, such as neutropenia and graft-versus-host disease.

**Why Each Wrong Option is Incorrect:**

**B. Chemotherapy:** Chemotherapy is a broad term for the use of drugs to kill rapidly dividing cells, including cancer cells. However, the cytotoxic effects of chemotherapy can also damage normal cells and tissues, leading to severe side effects. Chemotherapy is not specific to hairy cell leukemia cells and can harm other healthy cells as well.

**C. Radiotherapy:** Radiotherapy involves the use of ionizing radiation to damage DNA, leading to cell death. While radiotherapy can be effective in shrinking tumors and reducing symptoms, it is not specific to hairy cell leukemia cells. Hairy cell leukemia cells are not radiopaque, which means they cannot be effectively targeted by radiotherapy.

**D. Bone marrow transplantation:** Bone marrow transplantation, also known as hematopoietic stem cell transplantation, involves replacing a patient's damaged bone marrow with healthy stem cells from a donor. While bone marrow transplantation can be curative, it is a complex and risky procedure with high morbidity and mortality rates, and it is not a first-line treatment for hairy cell leukemia.

**Clinical Pearls:**

1. Rituximab is a more targeted treatment option for hairy cell leukemia, reducing the risk of severe side effects associated with chemotherapy and radiotherapy.
2. Hairy cell leukemia is characterized by the presence of hairy cells in the bone marrow, spleen, and lymph nodes, making Rituximab a more specific treatment option compared to chemotherapy and radiotherapy.
3. Hairy cell leukemia is a chronic disease, and bone marrow transplantation is not a first-line treatment due to its complexity, risk, and higher morbidity and mortality rates.
4. Radiotherapy is not effective in targeting hairy cell leukemia cells as they are not radiopaque.

**Core Principle:** Rituximab, a monoclonal antibody targeting CD20 antigen on B-cells, is a more targeted treatment for hairy cell leukemia compared to other options. In comparison, chemotherapy and radiotherapy are non-selective treatments