This article will help you read and understand your pathology report for mantle cell lymphoma.
by Rosemarie Tremblay-LeMay MD MSc FRCPC, updated on April 3, 2019
The immune system
Your immune system is made up of many different kinds of cells and each play an important role 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 small organs called lymph nodes. Lymph nodes are located throughout your body. Large numbers of immune cells can also be found in the blood, skin, gastrointestinal tract, and bones.
What is Mantle cell lymphoma?
Mantle cell lymphoma is a type of cancer that comes from immune cells called B-lymphocytes. In most cases, the cancer cells have a genetic change called a translocation involving the gene CCND1 (see Molecular tests below).
Lymphomas are divided into two groups called Hodgkin lymphoma and non-Hodgkin lymphoma. Mantle cell lymphoma is a type of non-Hodgkin lymphoma. The most common site involved is the lymph nodes, followed by the spleen and the bone marrow. Cancer cells are often also found in the blood. Other sites, such as the gastrointestinal tract, can be affected.
The diagnosis of Mantle cell 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.
Blastoid and pleomorphic cells
B-cell non-Hodgkin lymphomas are sometimes divided into three groups – small, medium, and large – based on the average size of the cancer cells. Mantle cell lymphoma is usually part of the small B-cell lymphoma category. The cancer cells are small to medium in size and most of the cells in the tumour look very similar to each other. However, there are two types of mantle cell lymphoma that are different and are important because they are associated with more aggressive behavior.
Your pathologist will perform a test called immunohistochemistry to better characterize the tumour and to exclude other diseases that can look similar to mantle cell 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 mantle cell lymphoma come from B-lymphocytes and they produce proteins normally made by B-lymphocytes such as CD20, PAX5 or CD79a. They also produce BCL2 and CD5. The cancer cells produce cyclin D1 in >95% of cases and it is a good marker for mantle cell lymphoma, as only few other types of lymphoma are positive for cyclin D1.
Another common protein is SOX11, which will also be positive in the few cyclin D1-negative cases. Other proteins commonly tested in the diagnosis of lymphomas, such as CD10, Bcl6 or LEF1, are usually negative.
Pathologists can also use immunohistochemistry to evaluate what is called the proliferation index. The proliferation index is a which is a measure of how fast the cancer cells are dividing to create new cancer cells. Ki-67 (also called MIB1) will be positive in cells that are in the process of dividing to produce more cells. In general, cancer that have a high proliferation index grow faster and behave more aggressively.
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 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 a 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 a cancer (a malignant tumour).
Mantle cell lymphoma is characterized by a translocation in the gene CCND1, which encodes the protein cyclin D1 (see Immunohistochemistry above). 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 tumor has been surgically removed. These tests are used to confirm the diagnosis of mantle cell lymphoma, which is especially useful if the results of the immunohistochemistry performed were not typical.