Burkitt's Lymphoma Health Article

Definition

Burkitt's lymphoma (BL) is a type of non-Hodgkin's lymphoma (NHL) that is sometimes called a B-cell lymphoma or small noncleaved cell lymphoma. It is an endemic (characteristic of a specific place) disease in central Africa but sporadic (occurring in scattered instances) in other countries. Burkitt's lymphoma is one of the most rapidly growing forms of human cancer. In addition, the number of new cases of this tumor is rising in most countries.

Description

Burkitt's lymphoma was first described in 1957 by Denis Parsons Burkitt, an Irish surgeon. While this type of lymphoma is still relatively rare in the United States, it is responsible for 50% of cancer deaths in children in Uganda and central Africa. The endemic form of Burkitt's lymphoma is characterized by rapid enlargement of the patient's jaw, loosening of the teeth, protruding eyeballs, or an abdominal tumor in the region of the kidneys or ovaries.

In the sporadic form of Burkitt's, the patient may have a facial tumor but is much more likely to have an abdominal swelling, often in the area of the ileocecal valve (the valve between the lower portion of the small intestine and the beginning of the large intestine). About 90% of American children with Burkitt's have abdominal tumors. Others may develop tumors in the testes, ovaries, skin, nasal sinuses, or lymph nodes. In adults, Burkitt's lymphoma frequently produces a bulky abdomen and may involve the liver, spleen, and bone marrow.

Demographics

In Western countries, Burkitt's lymphoma is more common in male than in female children. While the average age of patients with endemic Burkitt's is seven years, outside Africa the average age is closer to 11 years. In the United States, the non-Hodgkin's lymphomas as a group account for about 7% of cancers in persons under 20 years of age. Between 40% and 50% of these cases are Burkitt's lymphoma.

In adults, Burkitt's lymphoma is again more common in males than in females. It is 1, 000 times more common in persons with AIDS than in the general population. Currently, about 2% of AIDS patients develop Burkitt's lymphoma. The majority of these patients have stage IV disease by the time the tumor is diagnosed.

Causes and symptoms

Causes

ONCOGENES.

Burkitt's lymphoma affects a part of the immune system known as the lymphatic or lymphoid system. The lymphatic system is a network of tissues, glands, and channels that produces lymphocytes, a type of white blood cell. Some lymphocytes remain in clusters within the lymph nodes, while others circulate throughout the body in the bloodstream or in the lymph, which is a clear yellowish fluid carried by the lymphatic channels. Lymphocytes fall into two groups: T-cells, which regulate the immune system; and B-cells, which produce antibodies. Burkitt's lymphoma involves the B-cell lymphocytes. In 1982, researchers discovered an oncogene (a gene that can release cells from growth constraints, possibly converting them into tumors) in 90% of patients with Burkitt's lymphoma. Called the C-myc oncogene, it is responsible for the uncontrolled production of B-lymphocytes. It results from a translocation, or exchange, of genetic material between the long arm of human chromosome 8 and the long arm of human chromosome 14. In a smaller number of patients with Burkitt's, the translocation involves chromosomes 2 and 22 or chromosomes 2 and 8.

In the summer of 2000, researchers reported that a gene called the HMG-I/Y gene is also involved in the development of Burkitt's lymphoma. The C-myc onco-gene appears to stimulate the HMG-I/Y gene, which then triggers the changes in normal B-cells that cause them to multiply rapidly and form tumors.

VIRUSES.

In addition to translocations of genetic material, Burkitt's lymphoma is also associated with oncogenic viruses—the Epstein-Barr virus (EBV) in endemic Burkitt's and human immunodeficiency virus (HIV) in the sporadic form. EBV, or human herpesvirus 4, is the virus that causes infectious mononucleosis. The presence of EBV in patients with endemic Burkitt's has been interpreted as a side effect of the high rates of malaria in central Africa. African children may have immune systems that cannot fight off infection with EBV because they have been weakened by malaria. The children's B-lymphocytes then reproduce at an unusually high rate. Currently, however, the precise role of EBV in Burkitt's lymphoma is still being investigated, because the virus is less common in patients outside Africa. In the United States, about 25% of children and 40% of adult AIDS patients with Burkitt's have the Epstein-Barr virus.

Symptoms

In children, symptoms may appear as soon as four to six weeks after the lymphoma begins to grow. The more common symptom pattern is a large tumor in the child's abdomen accompanied by fluid buildup, pain, and vomiting. If the lymphoma begins in the blood marrow, the child may bleed easily and become anemic.

In adults, the first symptoms of Burkitt's lymphoma may include swelling in a lymph node in the upper body or a swollen and painful abdomen. If the tumor is located in the chest, it may put pressure on the airway and cause difficulty in breathing. There may be unexplained itching or weight loss. Other patients may have more general symptoms, such as fever or a loss of energy. Adults with AIDS often have tumors developing in several different locations in the body by the time they are diagnosed.