Lymphomas are cancers of the lymphoid tissue that is part of our body's immune system. Our immune system protects us from infection. It is a complex system made up of the bone marrow, the thymus gland (which lies behind the breast bone), the spleen and the lymph nodes (or lymph glands). One of the most important cells in our immune system is a type of white blood cell called a lymphocyte. There are two types of lymphocytes: 'B-cells' and 'T-cells'. All lymphocytes are produced in the bone marrow and start life as young, immature cells called stem cells. Some lymphocytes continue their development in the bone marrow or lymph nodes and these are called B-cells but others move to the thymus gland and they are called T-cells.
Many years ago it was thought that lymphomas could be divided into just two conditions: Hodgkin lymphoma (named after Thomas Hodgkin, the London doctor who first described it over 100 years ago) and non-Hodgkin lymphoma (NHL). With the passage of time it has become clear that NHL is not a single illness but includes a number of cancers, which behave very differently. The description and classification of the various types of NHL has developed over the years as more has been learnt both about the immune system and the cancers themselves. The most recent classification still recognises the difference between Hodgkin lymphoma and NHL but then goes on to divide NHL into some fifteen different tumour types.
From a practical viewpoint doctors divide all these various types of NHL into one of three groups: low grade, high grade or intermediate grade. This division is based on the appearances under the microscope and helps predict how the condition will behave. As the precise characteristics of each of the individual subtypes of NHL are becoming better understood this classification is gradually giving way to the idea that the various subtypes of NHL are different conditions in their own right. Each of these will have different patterns of behaviour from indolent to much more aggressive.
Low-grade NHL or indolent NHL usually has a relatively slow growth rate, running a long course and often needing little or no treatment for months or possibly years. When they do need treatment they respond well but are likely to come back again at some time in the future. They frequently respond to treatment on several occasions over the years but may eventually become resistant or transform to a high-grade form of NHL.
High-grade NHL or aggressive NHL usually grows more rapidly and behaves more aggressively and so needs immediate treatment. Despite this they are more likely to be completely cured than low grade NHL. Around half of all people with high-grade forms of NHL will be cured by the use of intensive chemotherapy.