Molecular Imaging Insight - May 2008 - (Page 4) A s diagnostic imaging and treatment options expand, the role of PET is expected to change. David Mankoff, MD, PhD, an associate professor of radiology at the University of Washington School of Medicine in Seattle is a leading expert in the use of state-of-the-art imaging to better diagnose cancer and guide treatment decisions. He explains the promise of PET in breast cancer staging and management. Dr. Mankoff also outlines a few pitfalls for practices to avoid. PET: The right information at the right time FDG-PET is the only form of molecular imaging currently used in breast cancer cases. Oncologists turn to PET to provide information for a number of indications, including staging, monitoring therapeutic response, and increasingly, to direct therapy, says Mankoff. “FDG-PET is extremely useful in staging advanced breast cancer and monitoring systemic response to therapy,” he continues. However, FDG-PET is not necessarily the right imaging study for all breast cancer patients. That is, not all breast cancers benefit from PET. PET’s utility hinges on the patient’s stage and the clinical questions asked. PET provides critical clinical data when used in staging recurrent or metastatic breast cancer and locally advanced breast cancer. Specifically, the modality can provide useful information about whether or not the cancer has spread to the lymph nodes and more distant sites. Another area where PET could play a pivotal role, says Mankoff, is monitoring response to therapy, especially in metastatic disease and bone-dominant metastatic breast cancer. In fact, PET may be currently under-utilized in metastatic cases. Traditionally, some referring oncologists avoided applying advanced imaging approaches to metastatic breast cancer because it is viewed as incurable. The definition of incurable, however, has evolved in the last decade, largely due to an increasing array of choices for systemic therapy of breast cancer, making PET an increasingly useful imaging tool in metastatic disease. “Patients with bone-dominant metastatic breast cancer can live many years after diagnosis, primarily due to the availability of improved therapeutic options,” Mankoff says. As the number of therapeutic options for metastatic breast cancer continues to grow, it becomes more important to determine whether or not a patient is responding to a specific therapy. “It’s a very important application for PET and PET/CT because other modalities can not always provide the necessary information to inform decisions about therapeutic response,” says Mankoff. “This is especially true in bone-dominant breast cancer.” “[Metastatic breast cancer] is a very important application for PET and PET/CT because other modalities can not always provide the necessary information to inform decisions about therapeutic response. This is especially true in bone-dominant breast cancer.” David Mankoff, MD, PhD, associate professor of radiology, University of Washington School of Medicine, Seattle The flip side: Over-utilization? “There are a few cases where some centers may use PET, even though it is unlikely to be helpful,” Mankoff says. Whole-body PET has not been shown to be useful in early stage breast cancer cases, particularly newly diagnosed stage 1 or early stage 2 patients. Oncologists may order a PET scan to determine if the Molecular Imaging Insight | May 2008 cancer has spread to the lymph nodes. “Some practices may order a PET scan just to see if there is any evidence of spread, sometimes to allay patients’ fears,” says Mankoff. But PET is not likely to be useful in newly diagnosed, early stage breast cancer. PET is not sufficiently sensitive for detecting an early cancer spread to axillary nodes compared to the current standard of care: sentinel lymph node mapping. “Studies comparing PET to sentinel lymph node mapping show that PET’s sensitivity can be as low as 20 to 40 percent. In other words, it misses 60 to 80 percent of nodal metastases in early breast cancer,” Mankoff points out. In addition, there is some potential for false positives on an early stage PET scan. “In these cases, PET has not been shown to be helpful or cost-effective,” he says. Sites that turn to PET in early-stage disease to address patient anxiety paradoxically risk increasing patient anxiety and delaying care if false findings occur. There is a related area where some centers may fall into the inappropriate use trap. In addition to axillary nodal staging, some centers may order a PET study for systemic staging of early breast cancer to determine if the disease has spread to distant sites. The problem, says Mankoff is two-fold. The spread to distant sites in early disease, especially in the absence of axillary modal spread, is rare. PET has not been widely studied for systemic staging for early-stage breast cancer; however, prior studies using other staging modalities such as CT and bone scan have not favored systemic staging for early disease, especially in the absence of axillary spread. “Some of the studies of systemic staging of early breast cancer report up to five or six false positives for every true positive,” Mankoff says. “Therefore, in the absence of symptoms, systemic staging is not recommended for early breast cancer. There is no reason to think findings would differ for FDG PET/CT, at least not in the absence of supporting data.” The upshot? PET is unlikely to provide helpful information in detecting regional spread to the lymph modes or metastatic spread beyond the axilla in early-stage disease. There are, however, circumstances where PET is useful in detecting regional spread to the lymph nodes in recurring or advanced breast cancer. “What’s needed are more studies and more education about instances in which PET is inappropriate and not helpful,” concludes Mankoff. One recent source for information is The National Comprehensive CanMolecularImaging.net http://MolecularImaging.net
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