Get a comprehensive understanding of the pathology and cellular features of hairy cell leukemia with detailed insights.

Hairy Cell Leukemia

Humza Khizer

Overview

Hairy cell leukemia (HCL) is a rare type of chronic lymphoid leukemia characterized by the presence of abnormal B-lymphocytes in the bone marrow, spleen, and peripheral blood. 
&nbsp;

Hairy cell leukemia ( HCL) is a rare disease, accounting for approximately 2% of all lymphoid leukemias<a href="#accordion">[1]</a>. The incidence of HCL varies between populations, with an estimated 1000 new cases being reported in the United States each year<a href="#accordion">[1]</a>.

The disease predominantly affects middle-aged men, with a male-to-female ratio of 4:1<a href="#accordion">[2]</a>. While it may also occur in younger individuals, the median age of diagnosis is approximately 55 years.

Hairy cell leukemia is characterized by the accumulation of mature B lymphocytes that exhibit distinct morphologic features with abundant cytoplasmic projections giving them a &quot;hairy&quot; or &quot;frayed&quot; appearance. HCL typically has an indolent course and can cause pancytopenia, infections, and splenomegaly. 
&nbsp;

There are no specific subtypes of hairy cell leukemia. 
&nbsp;

Signs and Symptoms

Some of the signs and symptoms of hairy cell leukemia include<a href="#accordion">[3]</a>:

<ul>
	<li>Fatigue and weakness</li>
	<li>Recurrent infections</li>
	<li>Fever</li>
	<li>Easy bruising and bleeding</li>
	<li>Enlarged spleen (splenomegaly)</li>
	<li>Enlarged liver (hepatomegaly)</li>
	<li>Abdominal discomfort or pain</li>
	<li>Weight loss</li>
	<li>Night sweats 
	&nbsp;</li>
</ul>

It&#39;s important to note that some patients with HCL may be asymptomatic at diagnosis and the disease may be detected incidentally during routine blood tests. 
&nbsp;

Causes

Hairy cell leukemia is a type of cancer that affects white blood cells, specifically B cells, which help fight germs in the body. The cause of hairy cell leukemia is not fully understood, but it is believed to be the result of changes in the DNA of B cells, which cause them to produce abnormal cells that do not function properly. These abnormal cells can accumulate and interfere with the production of healthy blood cells in the bone marrow and other organs, leading to symptoms such as swelling in the spleen, liver, and lymph nodes, increased risk of infections, easy bruising, and fatigue. 
&nbsp;

There is no routine screening test for hairy cell leukemia because it is a rare disease and most people with HCL are diagnosed after experiencing symptoms. However, people who have a family history of HCL or who have been exposed to certain chemicals, such as benzene or pesticides, may be at higher risk and should discuss their risk with their doctor. In these cases, regular blood tests may be recommended to monitor for any changes in blood cell counts. 
&nbsp;

Diagnosis

The diagnostic tests for hairy cell leukemia include: 
&nbsp;

<ol>
	<li>Physical Exam And History: The doctor will take a detailed history, inquiring about the patient&rsquo;s symptoms, health habits, past medical history, and any treatments they&rsquo;ve undergone. During the physical exam, the doctor will assess for swollen lymph nodes, any lumps, splenomegaly, hepatomegaly, and any other signs of disease.</li>
	<li>Blood Tests: Blood tests can show abnormalities in blood cell counts, such as low red blood cells (<a href="https://merisehat.pk/disease/anemia">anemia</a>), low platelets, and low or high white blood cells. A peripheral blood smear will reveal &lsquo;hairy&rsquo; cells.</li>
	<li>Bone Marrow Biopsy: A small sample of bone marrow is taken from the hip bone and examined under a microscope to look for the presence of hairy cells.</li>
	<li>Flow Cytometry: This test uses antibodies to identify specific markers on the surface of cells, including hairy cells.</li>
	<li>Immunohistochemistry: This test uses antibodies to identify specific proteins in tissue samples, including those found in hairy cells.</li>
	<li>Imaging Tests: Imaging tests, such as CT or PET scans, may be used to check for the enlargement of the spleen, liver, or lymph nodes, which can be a sign of HCL. 
	&nbsp;</li>
</ol>

There is currently no standard staging system for hairy cell leukemia<a href="#accrodion">[4]</a>. Doctors rely on the patient&rsquo;s test results to assess how far the cancer has progressed and create a treatment plan. 
&nbsp;

Treatment

Most people with hairy cell leukemia do not exhibit any symptoms. Therefore, doctors will often wait and see if the symptoms develop before starting treatment. Regular blood tests are required to assess if hairy cell leukemia is progressing. 
&nbsp;

The treatment of hairy cell leukemia (HCL) may include the following<a href="#accordion">[1]</a>:

<ol>
	<li>Chemotherapy: This is the main treatment for HCL and involves the use of drugs to kill the cancer cells. It is very effective and most people go into complete or partial remission</li>
	<li>Immunotherapy: This type of treatment uses drugs that help the body&#39;s immune system to recognize and attack cancer cells.</li>
	<li>Surgery: Surgery may be used in some cases to remove the spleen, which is often enlarged in people with HCL.</li>
	<li>Targeted Therapy: This type of treatment targets specific chemicals within cancer cells. Doctors may use it as a first-line treatment for hairy cell leukemia. Moreover, it can also be used with chemotherapy and for relapse cases.&nbsp; 
	&nbsp;</li>
</ol>

Hairy cell leukemia (HCL) can lead to a number of complications, some of which include: 
&nbsp;

<ul>
	<li>Infections: Individuals with HCL have an increased risk of developing infections due to a weakened immune system, which can be caused by the disease itself as well as certain treatments.</li>
	<li>Anemia: HCL can cause a decrease in red blood cells, leading to anemia. This can cause fatigue, weakness, and shortness of breath.</li>
	<li>Thrombocytopenia: HCL can cause a decrease in platelets, leading to thrombocytopenia. This can cause easy bruising and bleeding.</li>
	<li>Splenomegaly: HCL can cause the spleen to enlarge, which can cause abdominal discomfort or pain.</li>
	<li>Second Cancers: Individuals with HCL have an increased risk of developing second cancers, including other types of blood cancers. 
	&nbsp;</li>
</ul>

The exact causes of hairy cell leukemia are not yet fully understood. However, research has suggested that certain risk factors may play a role in the development of HCL. Some of the possible risk factors for HCL include<a href="#accordion">[1]</a> <a href="#accordion">[3]</a>: 
&nbsp;

Family History - A family history of HCL or other types of lymphoid malignancies increases the risk.

Age - It is more common in older adults in their 50s or 60s. It is rare in those younger than 30 years and children.

Gender - While both genders can be affected, men are more likely to develop HCL.

Ethnicity - White people have a higher risk of developing HCL. 
&nbsp;

It&#39;s important to note that not all individuals with these risk factors develop HCL, and HCL can occur in individuals with no known risk factors. 
&nbsp;

There are currently no known preventive factors for hairy cell leukemia, as the exact causes of the disease are not yet fully understood. However, some studies have suggested that avoiding exposure to certain chemicals and toxins, such as benzene and pesticides, may reduce the risk of developing HCL<a href="#">[5]</a>. 
&nbsp;

In 2018, the U.S. Food and Drug Administration (FDA) approved moxetumomab pasudotox-tdfk for use in adults with relapsed or refractory hairy cell leukemia.<a href="#accordion">[6]</a>&nbsp; &nbsp;

This is a type of immunotoxin that targets the CD22 protein on the surface of HCL cells, causing them to die. It was tested in a phase III clinical trial, which included 80 patients with relapsed or refractory HCL. The trial showed that the drug was highly effective, with an overall response rate of 75%, including a complete response rate of 41%.

The study also found that moxetumomab pasudotox had a manageable safety profile, with the most common adverse events being fever, nausea, and fatigue. 
&nbsp;

Key Points

<ul>
	<li>Hairy cell leukemia (HCL) is a rare type of chronic lymphoid leukemia characterized by the presence of abnormal B-lymphocytes, called hairy cells, in the bone marrow, spleen, and peripheral blood.</li>
	<li>Hairy cell leukemia is a rare disease, accounting for approximately 2% of all adult leukemias</li>
	<li>Some of the signs and symptoms of hairy cell leukemia include fatigue and weakness, recurrent infections, fever, easy bruising, and bleeding</li>
	<li>&nbsp;The cause of hairy cell leukemia is not fully understood, but it is believed to be the result of changes in the DNA of B cells, which cause them to produce abnormal cells that do not function properly.</li>
	<li>&nbsp;There is no routine screening test for hairy cell leukemia because it is a rare disease and most people with HCL are diagnosed after experiencing symptoms.</li>
	<li>&nbsp;Blood tests can show abnormalities in blood cell counts, such as low red blood cells (anemia), low platelets, and low or high white blood cells.</li>
	<li>&nbsp;Imaging tests, such as CT or PET scans, may be used to check for the enlargement of the spleen, liver, or lymph nodes, which can be a sign of HCL.</li>
	<li>Chemotherapy is the main treatment for HCL and involves the use of drugs to kill cancer cells.</li>
	<li>Surgery may be used in some cases to remove the spleen, which is often enlarged in people with HCL.</li>
	<li>&nbsp;Individuals with HCL have an increased risk of developing infections due to a weakened immune system.</li>
	<li>There are currently no known preventive factors for hairy cell leukemia, as the exact causes of the disease are not yet fully understood.</li>
	<li>Moxetumomab pasudotox is a type of immunotoxin that targets the CD22 protein on the surface of HCL cells, causing them to die. The FDA approved its use for the treatment of refractory or relapsed HCL in 2018. 
	&nbsp;</li>
</ul>

[1] Naing PT, Acharya U, Kumar A. Hairy Cell Leukemia. [Updated 2022 May 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

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