Burkitt lymphoma is a type of cancer that comes from immune cells called B-lymphocytes. It is characterized by a genetic change called a translocation involving the gene MYC (see Molecular tests below). This genetic change allows the cancer cells to divide and create new cancer cells very quickly.
Lymphomas are divided into two groups called Hodgkin lymphoma and non-Hodgkin lymphoma. Burkitt lymphoma is a type of non-Hodgkin lymphoma. Unlike many other lymphomas, Burkitt lymphoma tends to start outside the lymph nodes, which are small immune organs located throughout the body. The parts of the body often involved by Burkitt lymphoma include the bones of the face and the long bones of the arms and legs, the gastrointestinal tract, gonads, kidneys, and breasts. Other sites including the brain and spinal cord may also be involved. Cancer cells can also be found in the blood.
Your immune system is made up of many different kinds of cells and each plays an important role in protecting your body from infections and helping you heal after an injury. Unlike other types of organs, your immune system is spread throughout your body. Most immune cells are found in lymph nodes, although many are also found in the blood, skin, gastrointestinal tract, and bones.
There are three clinical subtypes of Burkitt lymphoma, called endemic, sporadic and immunodeficiency-associated. Each subtype is found in a different situation.
Some cases of Burkitt lymphoma are associated with the Epstein Barr Virus (EBV), most frequently in the endemic variant.
The diagnosis of Burkitt lymphoma is usually made after a small piece of tissue is removed in a procedure called a biopsy. The tissue is then sent to your pathologist who examines it under the microscope. Burkitt lymphoma cells divide to create new cancer cells quickly. For this reason, the tumour can be quite large at the time of diagnosis.
Your pathologist will perform a test called immunohistochemistry to better understand the tumour and to exclude other diseases that can look similar to Burkitt lymphoma under the microscope. Immunohistochemistry is a test that uses antibodies to highlight different types of proteins produced by cells. When the cells produce a protein, pathologists describe the result as positive or reactive. When the cells do not produce the protein, the result is described as negative or non-reactive.
The cancer cells in Burkitt lymphoma come from B-lymphocytes and they produce proteins normally made by B-lymphocytes such as CD20, PAX5 or CD79a. They also produce CD10 and BCL6. The cancer cells produce MYC in almost all cases. Other markers commonly used in the diagnosis of B-cell lymphomas, such as CD5, CD23 or BCL2, are negative.
Pathologists can also use immunohistochemistry to determine how fast the cancer cells are dividing to create new cancer cells. This is called the proliferation index. Ki-67 (also called MIB1) will be positive in cells that are in the process of dividing to produce more cells. The cells of Burkitt lymphoma divide quickly and Ki-67 will be positive in almost all the cells. For this reason, the proliferation index is usually close to 100%.
B-cell non-Hodgkin lymphomas are often divided into three groups – small, medium, and large – based on the size of the typical cancer cell in the tumour. Burkitt lymphoma is part of the group with cells of medium size. Most of the cells in the tumour typically look very similar to each other.
When examined under the microscope, many dividing cancer cells will be seen. Your pathologist will also see lots of dying cancer cells. A type of immune cell called a macrophage will remove the dying cancer cells. Pathologists call the look of macrophages surrounded by cancer cells “starry-sky” because the macrophages are very light in colour while the cancer cells are dark blue (see image above).
Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce a piece of the machine called a protein.
Sometimes, a piece of DNA falls off one chromosome and becomes attached to a different chromosome. This is called translocation and it can result in the cell making a new and abnormal protein. If the new protein allows the cell to live longer than other cells or spread to other parts of the body, the cell can become cancer.
Burkitt lymphoma is characterized by a translocation in the gene MYC, which creates a protein by the same name that can be seen by immunohistochemistry. Pathologists usually test for these molecular changes by performing fluorescence in situ hybridization (FISH) on a piece of the tissue from the tumour. This type of testing can be done on the biopsy specimen or when your tumour has been surgically removed. This test can be used to help confirm the diagnosis of Burkitt lymphoma.