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Lymphomas- definition, types, lymphatic system

INTRODUCTION

Lymphoma is a type of cancer involving cells of the immune system, called lymphocytes, and therefore of lymphoid origin. These tumors usually start in lymph nodes but can involve lymphoid tissue in the spleen, the gastrointestinal tract (e.g. the wall of the stomach), the liver, or the bone marrow. They are often classified according to the degree of cell differentiation and the origin of the predominant malignant cell. Just as cancer represents many different diseases, lymphoma represents many different cancers of lymphocytes — about 35 different subtypes, in fact.

Lymphatic System Overview

  1. Lymph nodes are small collections of lymph tissue that occur throughout the body. The lymphatic system involves lymphatic channels that connect thousands of lymph nodes scattered throughout the body. Lymph flows through the lymph nodes, as well as through other lymphatic tissues including the spleen, the tonsils, the bone marrow, and the thymus gland.
  2. These lymph nodes filter the lymph, which may carry bacteria, viruses, or other microbes. At infection sites, large numbers of these microbial organisms collect in the regional lymph nodes and produce the swelling and tenderness typical of a localized infection. These enlarged and occasionally confluent collections of lymph nodes (so-called lymphadenopathy) are often referred to as “swollen glands.” In some areas of the body (such as the anterior part of the neck), they are often visible when swollen.
  3. Lymphocytes recognize infectious organisms and abnormal cells and destroy them. There are two major subtypes of lymphocytes: B lymphocytes and T lymphocytes also referred to as B cells and T cells.
    • B lymphocytes produce antibodies. Antibodies essentially alert other cells of the immune system to recognize and destroy these intruders, also known as pathogens (humoral immunity).
    • T cells, when activated, can kill pathogens directly. T cells also help in the mechanisms of immune system control, to prevent the system from inappropriate overactivity or underactivity (cell mediated immunity).
    • After fighting off an invader, some of the B and T lymphocytes “remember” the invader and are prepared to fight it off if it returns.

lymph nodes

DEFINITION OF LYMPHOMAS

Lymphoma is a group of cancers that affect the cells that play a role in the immune system and primarily represent cells involved in the lymphatic system of the body. Cancer occurs when normal cells undergo a transformation whereby they grow and multiply uncontrollably. Lymphoma is a malignant transformation of either B or T cells or their subtypes.

CLASSIFICATION OR TYPES OF LYMPHOMAS

Lymphomas fall into one of two major categories: Hodgkin’s lymphoma (HL, previously called Hodgkin’s disease) and all other lymphomas (non-Hodgkin’s lymphomas or NHLs).

  1. These two types occur in the same places, may be associated with the same symptoms, and often have similar appearance on physical examination. However, they are readily distinguishable via microscopic examination.
  2. Hodgkin’s disease develops from a specific abnormal B lymphocyte lineage. NHL may derive from either abnormal B or T cells and are distinguished by unique genetic markers.
  3. There are five subtypes of Hodgkin’s disease and about 30 subtypes of non-Hodgkin’s lymphoma.
  4. Because there are so many different subtypes of lymphoma, the classification of lymphomas is complicated (it includes both the microscopic appearance as well as genetic and molecular markers).
  5. Many of the NHL subtypes look similar, but they are functionally quite different and respond to different therapies with different probabilities of cure. HL subtypes are microscopically distinct, and typing is based upon the microscopic differences as well as extent of disease.

Lymphoma is the most common type of blood cancer in the United States. It is the seventh most common cancer in adults and the third most common in children. Non-Hodgkin’s lymphoma is far more common than Hodgkin’s lymphoma.

  1. In the United States, about 66,000 new cases of NHL and 8,500 new cases of HL were expected to be diagnosed in 2010, and the overall incidence is increasing each year.
  2. About 20,000 deaths due to NHL were expected in 2010 as well as 1,300 deaths due to HL, with the survival rate of all but the most advanced cases of HL greater than that of other lymphomas.
  3. Lymphoma can occur at any age, including childhood. Hodgkin’s disease is most common in two age groups: young adults 16-34 years of age and in older people 55 years of age and older. Non-Hodgkin’s lymphoma is more likely to occur in older people.
  4. The incidence of NHL has increased dramatically over the past decade; it is now the fourth most common type of cancer diagnosed in the United States and the fifth most common cause of cancer death. The incidence increases with each decade of life; the average age at diagnosis is 50 to 60 years.

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