Molecular Imaging News
August 18, 2005
Further Evidence that PET Scans Can Help Predict Outcomes in Non-Hodgkin’s Lymphoma
Annals of Oncology
According to an article published in the September issue of the Annals of Oncology, results from a positron emission tomography (PET) scan can help predict outcomes for patients diagnosed with non-Hodgkin?s lymphoma. Patients with a predicted poorer outcome may wish to undergo more aggressive therapy than those predicted to have optimal outcomes.
Non-Hodgkin?s lymphoma (NHL) is a form of cancer that begins in the cells of the lymph system, which includes the spleen, thymus, tonsils, bone marrow, lymph nodes, and circulating immune cells. Lymphocytes are the main cells in the lymph system and exist in two forms: B and T-cells. Each of these cells serves a specific function in aiding the body fight infection. In NHL, an excessive amount of atypical (cancerous) lymphocytes accumulates in the lymph system. These lymphocytes can crowd and suppress the formation and function of other immune and blood cells. NHL is categorized by the type of lymphocyte it involves and further defined by the rate at which the cancer grows. The appearance of the cells under a microscope indicates the growth rate. High-grade or aggressive NHL grows quickly, whereas low-grade or indolent lymphoma develops slowly. Lymphoma that has returned following therapy is classified as recurrent; refractory lymphoma is cancer that has stopped responding to standard therapies.
A current area of research involves efforts to individualize treatment in order to provide optimal outcomes for all patients. Although standard therapeutic approaches exist for different types of NHL, it is not clear why some patients respond to certain treatments while others may not. A process where scans follow initial cycles of treatment to test anti-cancers responses to treatment is currently being evaluated. Patients who appear to be responding well to treatment may continue with the treatment, while others who are not responding as well may alter their treatment strategy or try a more aggressive approach. Researchers are trying to appropriately match different types of scans with various cancers to provide information that may alter the course of care.
The use of PET scans may help doctors more accurately detect the presence and location of cancer cells. A PET scan is similar to a CT scan; however, PET scans can detect live cancer tissue. Prior to a PET scan, the patient receives an injection with substance that contains a type of sugar attached to a radioactive isotope. The cancer cells "take up" the sugar and attached isotope, which emits positively charged, low energy radiation (positrons). The positrons react with electrons in the cancer cells to produce gamma rays. The gamma rays are then detected by the PET machine, which transforms the information into a picture. If no gamma rays are detected in the scanned area, it is unlikely that the mass in question contains living cancer cells.
Researchers from London recently conducted a clinical trial to evaluate the effectiveness of a PET scan in NHL. This trial included 121 patients who underwent a PET scan following two to three cycles of chemotherapy. The response to therapy according to PET results corresponded with a patient?s progression-free survival and overall survival at 5 years. Of the patients whose results from PET scans were considered negative (good responses to therapy), a majority (89%) were alive without disease progression at 5 years. Conversely, among those whose PET scan results were considered positive (poor response to therapy), progression-free survival was only 16% at 5 years. The associations between PET results and PFS at 5 years were made independently of other factors that typically indicate prognosis (such as stage of disease).
The researchers concluded that PET scans following two to three cycles of chemotherapy may help to guide treatment options in aggressive NHL. Those with a poorer prognosis according to their PET scan results may wish to undergo alternative therapeutic approaches for optimal outcomes, while those with a good prognosis according to their PET scan may wish to continue with planned therapy. Although further studies are required regarding the clinical utility of PET scans in aggressive NHL, patients with this disease may wish to speak with their physician regarding their individual risks and benefits of undergoing a PET scan, as well as altering their therapeutic strategy should their results indicate a poor prognosis.