What is Hodgkin lymphoma?
Hodgkin lymphoma (formerly called Hodgkin’s Disease) is a type of cancer that starts from specialized immune cells called B-lymphocytes. Hodgkin lymphoma can start anywhere in the body where immune cells are normally found but it typically starts in the lymph nodes in the neck, chest, or under the arms.
The immune system
Your immune system is made up of many different kinds of cells and each plays an important role in protecting your body from infections and helping you heal after an injury. Unlike other types of organs, your immune system is spread throughout your body. Most immune cells are found in small organs called lymph nodes. Lymph nodes are located throughout your body. Large numbers of immune cells can also be found in the blood, skin, gastrointestinal tract, and bones. Normal B-lymphocytes are small cells that help your body fight off infections.
How do pathologists make this diagnosis?
The diagnosis of Hodgkin lymphoma can be made after a tissue sample is examined under the microscope by a pathologist. Unlike normal immune system tissue, Hodgkin lymphoma is made up of abnormal B-lymphocytes called Reed-Sternberg cells (or HRS cells). Reed-Sternberg cells are usually easy to recognize through a microscope because they are much larger than normal lymphocytes and the nucleus in the centre of the cell has two or more lobes.
The number of Reed-Sternberg cells are used to divide Hodgkin lymphomas into 2 main groups:
- Classic Hodgkin lymphoma – Lots of Reed-Sternberg cells are seen in this group. Classic Hodgkin lymphoma usually only involves lymph nodes and is rarely seen spreading to other organ systems. This group is further divided into several subtypes (see Types of Hodgkin lymphoma below).
- Nodular lymphocyte-predominant Hodgkin lymphoma – Very few or no Reed-Sternberg cells are seen in this group of Hodgkin lymphoma.
Immunohistochemistry is routinely performed on cases of Hodgkin lymphoma to confirm the diagnosis and to exclude other diseases that have a similar appearance under the microscope. This test allows pathologists to learn more about the types of proteins made by specific cells. Cells that produce a protein are called positive or reactive. Cells that do not produce a protein are called negative or non-reactive.
Classic Hodgkin lymphoma typically shows the following immunohistochemistry results:
- CD45 – Negative.
- CD30 – Positive.
- CD15 – Positive.
- CD20 – Negative.
- PAX5 – Positive.
- CD68 – Positive but only in the normal background cells.
- CD3 – Positive but only in the normal background cells.
Types of Classic Hodgkin lymphoma
Classic Hodgkin lymphoma (CHL) is a cancer group that includes several different lymphoma subtypes. Your pathologist determines the subtype by examining the tumour cells under the microscope.
The subtypes of classic Hodgkin lymphoma include:
- Nodular sclerosis (NSCHL) – This is the most common type of classic Hodgkin lymphoma. It accounts for 60%–80% of all cases. It typically occurs in people between 15 and 34 years old and those over 55 years old but can occur in people of any age. The incidence of NSCHL is about the same in men and women. The tumour cells in NSCHL grow in a nodular pattern which looks like large groups of cancer cells separated by a type of scar tissue called fibrosis.
- Mixed cellularity (MCCHL) – This is the second most common type of classic Hodgkin lymphoma. It accounts for 20%-25% of all cases. The number of patients with this type of lymphoma is higher in parts of the world outside of Canada and the United States, including Asia. Although it can occur in people at any age, it is most common in adults between the ages of 55 and 74, as well as children under the age of 14. MCCHL is more common in men than women with about 70% of patients being men. The tumour cells in MCCHL vary in shape and size and many of the large abnormal Reed-Sternberg cells are usually seen. Unlike NSCHL, a type of scar tissue called fibrosis is not seen in this type of lymphoma. A virus called the Epstein-Barr Virus (EBV) is sometimes found inside the tumour cells. MCCHL is an aggressive cancer, however, the prognosis for many patients is good.
- Lymphocyte-rich (LRCHL) – This type of classic Hodgkin lymphoma is much less common than the other subtypes and accounts for approximately 5% of all cases. It usually occurs in the upper half of the body and is rarely found in more than a few lymph nodes. People affected by this type of lymphoma are usually older than seen in other types of classic Hodgkin lymphoma. LRCHL is seen in men or women, although it is about twice as common in men.
- Lymphocyte-depleted (LDCHL) – This type of classic Hodgkin lymphoma is the least common subtype and accounts for less than 1% of all cases Similar to MCCHL, Epstein Barr Virus (EBV) is often found inside the cancer cells. LDCHL can affect both men and women but is most commonly seen in men between 30 – 71 years old. Unlike other forms of classic Hodgkin lymphoma, LDCHL can start in the abdomen and bone marrow although lymph nodes anywhere in the body can also be involved.
Rarely, Hodgkin lymphoma can change into another type of lymphoma. This type of change is called transformation. When transformation occurs, it is usually from nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) to diffuse large B-cell lymphoma (DLBCL).
by Philip Berardi, MD PhD FRCPC (updated July 16, 2021)