Researchers have discovered genetic mutations that may contribute to the development of an aggressive form of non-Hodgkin's lymphoma. These findings provide insight into a mechanism that cancer cells may use to survive, thus identifying potential new targets for treatment of the disease. The study conducted by researchers at the National Cancer Institute (NCI), the National Institute for Allergy and Infectious Diseases, and the National Human Genome Research Institute, components of the National Institutes of Health, and colleagues appeared January 7, 2010,in Nature.

Diffuse large B-cell lymphoma (DLBCL) originates in B cells, which are antibody-producing immune cells and one of the body's key defense mechanisms. DLBCL is the most common form of non-Hodgkin's lymphoma and represents about 30 percent of newly diagnosed cases. There are different subtypes of DLBCL that vary biologically and differ significantly in their rates of patient survival following chemotherapy. The activated B cell-like (ABC) subtype is the least responsive to currently available therapies.

When a normal B cell encounters a foreign substance, proteins on the cell surface known as B cell receptors (BCR) activate signalling pathways that tell the cell to survive and proliferate. A signalling pathway is a stepwise series of biochemical events that help regulate important cellular functions, such as proliferation and survival. Each pathway contains points at which normal signalling can become altered, causing cells to function abnormally. Alterations in signalling pathways have been found in many types of cancer cells. Previous research had suggested that BCR signalling might contribute to the development of lymphomas; however, direct genetic and functional evidence was lacking.

In the new study, researchers first used advanced laboratory techniques to identify critical points in the BCR signalling pathway that affect the survival of lymphoma cells. They found that interference with several individual components of this pathway caused lymphoma cells to die. Thus, ongoing BCR signalling -- which the authors refer to as chronic active signalling -- is necessary for ABC subtype DLBCL cell survival.

The team then looked for mutations in genes that encode these signalling pathway components in human DLBCL tumours. They found that about one-fifth of ABC subtype tumours had mutations in a BCR signalling component known as CD79B. The mutations increased BCR signalling by blocking a braking process that normally turns off the pathway in response to inhibitory signals.

"Our data provide important evidence that BCR signalling plays a crucial role in ABC DLBCL," said study senior author Louis M. Staudt. M.D., Ph.D., of NCI's Center for Cancer Research. "As such, this study opens up a wealth of therapeutic opportunities for this type of lymphoma and may eventually lead to clinical trials testing agents that target components of the BCR signalling pathway." Indeed, the Staudt team found that dasatinib, a drug that is approved for the treatment of chronic myelogenous leukaemia, could turn off BCR signalling by inhibiting the activity of one of the pathway's components, a protein called BTK, thereby killing ABC subtype DLBCL cells that exhibit chronic active BCR signalling.

"However, more research is needed to understand the various biochemical mechanisms by which chronic, active BCR signalling begins," said Staudt. "Tests will also need to be developed that can identify patients with cases of DLBCL that depend on chronic, active BCR signalling, so that we can rationally develop clinical trials with agents that inhibit the BCR pathway."

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