Lymphoma is a type of cancer that involves immune system cells called lymphocytes. Just as cancer is a blanket term for a number of different diseases, lymphoma represents around 35 different types of cancer in which lymphocytes grow and multiply uncontrollably.
According to Cancer Research UK, around, 12,783 people in the UK are diagnosed with non-Hodgkin lymphoma each year and the condition results in around 4,676 deaths a year.
Around 1,845 people in the UK are diagnosed with Hodgkin lymphoma each year with the condition leading to 328 deaths a year.
Lymphoma can occur at any age, including childhood. Hodgkin’s lymphoma is most common in young adults aged 15-35 years and in people over 50 years old. Non-Hodgkin’s lymphoma is more likely to affect older people, with the average age of diagnosis being around 65 years old.
Lymphocytes are white blood cells in lymph that recognise and prepare for attack by - or in some cases attack directly - infectious agents and abnormal cells that could turn cancerous. There are two main types: B lymphocytes and T lymphocytes, also known as B cells and T cells.
In lymphoma, abnormal B or T cells (or their subtypes) may first accumulate in one or more lymph nodes or in other lymphatic tissues such as the spleen, forming a mass or tumour as they continue to multiply.
Lymph nodes are small collections of lymph tissue distributed throughout the body and connected by lymphatic channels. They can be enlarged by cancer but also by bacterial or viral infections, which produces the familiar symptom of ‘ swollen glands’.
In lymphoma, the abnormal lymphocytes may travel from one lymph node to the next, spread to other lymphatic tissues or travel to remote organs almost anywhere in the body. When lymphoma spreads outside lymphatic tissue, it is known as extranodal disease.
Types of lymphoma
Lymphomas fall into one of two main categories. Hodgkin's lymphoma (HL, previously called Hodgkin’s disease) and all other lymphomas (non-Hodgkin's lymphomas or NHLs).
Non-Hodgkin’s lymphoma is far more common, accounting for between 55% and 60% of all malignant lymphomas. Hodgkin’s lymphoma develops from a specific abnormal type of B lymphocyte, whereas NHL may start with abnormal growth of B or T cells.
The two types of lymphoma can occur in the same places, may generate the same symptoms, and often have similar physical characteristics. However, they are easily distinguishable through a microscopic examination.
Classifying lymphomas is complicated, though. There are five different subtypes of Hodgkin’s lymphoma and some 30 subtypes of non-Hodgkin’s lymphoma. Many of the NHL subtypes look similar but they function quite differently and respond to different therapies, with different odds of a cure.