Hodgkin's Lymphoma Classification

Hodgkin’s lymphoma is a form of cancer that affects the lymphatic system. This condition is also referred to as Hodgkin’s disease.

Lymphoid tissue is largely composed of white blood cells called lymphocytes. Lymphocytes can be divided into main types: the B lymphocytes or B cells and the T lymphocytes or T cells. The B lymphocytes provide protection against pathogens such as bacteria and viruses through the production of antibodies, which attach to the germs and flag them up for destruction by the immune system. The T lymphocytes can be divided into several specialized groups. Some T lymphocytes target specific cells or bacteria that have been infected with a fungi or virus, while other types are involved in regulating the activity of other cells of the immune system. Almost all cases of Hodgkin’s lymphoma originate in the B lymphocytes.

Lymphoma can be divided into two main types: Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. Hodgkin’s lymphoma only accounts for around one fifth of the lymphomas diagnosed each year which translates to just over 1600 people in the UK annually.

The type of lymphoma a patient has is determined based on microscopic examination of a lymph node biopsy. In the case of Hodgkin’s lymphoma, a particular type of cell called the Reed-Sternberg cell is usually present. The Reed-Sternberg cell is not usually found in other forms of lymphoma, which are therefore referred to as non-Hodgkin’s lymphoma. The Reed-Sternberg cell is a B lymphocyte that has become cancerous. On examination, these cells appear much larger than healthy lymphocytes and also look different to the cells seen in non-Hodgkin’s lymphoma and other forms of cancer. In classic Hodgkin’s lymphoma, the lymph nodes are enlarged and contain a small number of Reed-Sternberg cells surrounded by a large number of healthy immune cells. The Reed-Sternberg cells also usually contain two nuclei.

Hodgkin’s lymphoma and non-Hodgkin’s lymphoma behave and spread differently, so it is important to differentiate between them so that the correct treatment approach can be selected. Classic Hodgkin’s lymphoma can be categorised into four different subtypes, according to the Reed-Sternberg cell morphology and the cell composition that occurs around the Reed-Sternberg cells. These subtypes are described below:

Nodular sclerosis

This is the most commonly occurring form of Hodgkin’s lymphoma, accounting for between 60% and 80% of all cases diagnosed. This subtype is usually diagnosed at an early stage when enlarged lymph nodes in the neck are investigated. On examination of lymph node biopsy, large tumor nodules display scattered Reed-Sternberg cells among reactive lymphocytes, plasmocytes and eosinophils. Collagen fibrosis is present to varying degrees.

Mixed cellularity

This is the second most common form of the disease and accounts for around 5% of Hodgkin’s lymphomas diagnosed. The mixed-cellularity subtype mostly develops in older adults, although it can develop at any age. On diagnosis, a few different groups of lymph nodes are usually affected and feature numerous Reed-Sternberg cells amongst lymphocytes, plasmocytes, histiocytes and eosinophils. Previous infection with Epstein Barr virus is commonly associated with this subtype. The mixed-cellularity subtype is sometimes confused with the early phase of the nodular sclerosis subtype. Although this subtype can affect any lymph node, it usually develops in the upper body parts.

Lymphocyte-rich subtype

This subtype is rare and accounts for about 5% of Hodgkin’s lymphoma cases. When the lymph node tissue is examined under a microscope, many very small lymphocytes and only very few Reed-Sternberg cells are seen. The lymphocyte-rich subtype typically occurs in the upper half of the body and usually involves only a few lymph nodes. This subtype is associated with the most favorable prognosis.

Lymphocyte-depleted subtype

This is the least common subtype, accounting for less than 1% of cases. It mainly affects older individuals. On microscopic examination of the lymph node tissue, there is an abundance of pleomorphic Reed-Sternberg cells and few reactive lymphocytes. This disease is more likely to be at an advanced stage by time it is diagnosed and usually involves lymph nodes in the abdomen, liver, spleen and bone marrow.

Nodular lymphocyte predominant type

According to the present classification, nodular lymphocyte predominant Hodgkin’s lymphoma is not included as a form of classic Hodgkin’s lymphoma. The primary difference between this and classic forms of Hodgkin’s disease is that very few Reed-Sternberg cells are seen in the nodular lymphocyte predominant type. Other abnormal cells referred to as “popcorn cells” are also present. On diagnosis, only one group of lymph nodes is affected and the lymphoma tends to be slower growing than in classic Hodgkin’s lymphoma. The nodular lymphocyte predominant subtype only accounts for around 5% of Hodgkin’s lymphoma cases. It can occur at any age, although it is more common among older individuals and more common among men than among women.