Lymphomas are malignant neoplasms (tumours that tend to grow, invade and spread) of the lymphoid lineage. A Lymphoma refers to a group of cancers of the lymph system which is part of the body's immune system. The immune system protects the body from foreign substances, infection and diseases. The lymph system is made up of lymph nodes, the spleen and the thymus (which produce and store infection-fighting cells) as well as other body areas that have collections of white blood cells within them such as the tonsils, stomach, small intestine and skin. Lymphoma affects a type of white blood cells known as lymphocytes. It occurs when lymphocytes grow and multiply uncontrollably.
Lymphoma can be broadly classified as either Hodgkin Lymphoma (Hodgkin's disease), or as non-Hodgkin Lymphoma. They can present in similar ways but are very different in the way they spread around the body, affect the body and respond to treatment. The presence of an abnormal cell called a Reed-Sternberg cell means it is Hodgkin Lymphoma while the absence means it is non-Hodgkin Lymphoma. Lymphoma, both Hodgkin lymphoma and non-Hodgkin Lymphoma combined, is the third most common cancer in children.
Hodgkin Lymphoma
Hodgkin Lymphoma is classically described as a B-lineage Lymphoma, characterised by the existence of Reed-Sternberg cells and lymphocytic infiltration (red patches and lumps on the face and body). Infections with the Epstein-Barr virus have also been implicated in the development of Hodgkin Lymphoma along with autoimmunity and immunodeficiency.
Hodgkin Lymphoma has a unique bimodal age distribution that differs geographically, meaning that there are two different peak periods during which a person may contract the disease. In developed countries such as Singapore, the early peak occurs in the mid to late 20s and the second peak occurs after the age of 50. The difference in developing countries is that the early peak occurs before adolescence (before 12 or 13 years old).
There are two major types of childhood Hodgkin Lymphoma:
1. Classical Hodgkin Lymphoma
There are four major sub-types in classical Hodgkin Lymphoma which are based on how the cancer cells look under a microscope:
- Lymphocyte-rich classical Hodgkin Lymphoma
- Nodular sclerosis Hodgkin Lymphoma
- Mixed cellularity Hodgkin Lymphoma
- Lymphocyte-depleted Hodgkin Lymphoma
2. Nodular lymphocyte-predominant Hodgkin Lymphoma
Non-Hodgkin Lymphoma
Non-Hodgkin Lymphoma can generally occur at any time throughout childhood and adolescence but is more commonly found in young children below 10 years of age as compared to Hodgkin Lymphoma.
There are three major types of non-Hodgkin Lymphoma found in children – mature B-cell Lymphoma, precursor lymphoid Lymphoma and mature T-cell Lymphoma.
Mature B-cell Lymphoma
This is the most common type of non-Hodgkin Lymphoma which involves the B-lymphocytes of the immune system. These Lymphomas make up about 40% of non-Hodgkin lymphoma cases1. Children with this type of non-Hodgkin Lymphoma usually have enlarged lymph nodes in the throat, neck or in the abdomen. It may be found in the bones or bone marrow. There are three major subtypes:
- Burkitt's Lymphoma (BL)
- Diffuse large B-cell Lymphoma (DLBCL)
- Primary mediastinal B-cell Lymphoma (PMBL)
Mature B-cell Lymphoma develops from B-cells in the mediastinum (the area behind the breastbone). It may spread to nearby organs including the lungs and the sac around the heart. It may also spread to lymph nodes and distant organs including the kidneys. This Lymphoma occurs more frequently in older adolescents.
Precursor Lymphoid Lymphoma
Precursor Lymphoid Lymphoma, also known as Lymphoblastic Lymphoma, refers to either T-cell or B-cell and accounts for about 30% of non-Hodgkin Lymphoma in children1. It can cause swollen lymph nodes or glands in any part of the body. Some children with Lymphoblastic Lymphoma may have a large mass (tumour) in the mediastinum. Lymphoblastic Lymphoma can also invade the bone marrow or spinal fluid.
If there are more than 25% blasts in the bone marrow by convention, it is defined as Acute Lymphoblastic Leukaemia (ALL).
Mature T-cell Lymphoma
Anaplastic Large Cell Lymphoma (ALCL) and Peripheral T-cell Lymphoma (PTCL) make up the mature T-cell Lymphomas but PTCL is very rare. ALCL commonly involves lymph nodes and glands but may also occur in bones and primary organs. About 10% of childhood non-Hodgkin Lymphoma is caused by ALCL2. ALCL may also cause rashes or lumps in the skin. It is often rapidly growing and causes severe inflammation in the body. As a result, the child may have symptoms such as high fevers or loss of weight and appetite.
There is no known cause of Lymphoma in children. However, certain risk factors may cause a child to be more vulnerable and thus contract Lymphoma.
Children who are born with or acquire conditions that affect the immune system are more likely to develop Lymphoma. Having a sibling with Lymphoma also slightly raises a child's risk. Prior infection with the Epstein-Barr virus is also associated with a greater risk for Lymphoma. There are no known environmental toxins that increase the risk of Lymphoma in children.