Breast Cancer: When Molecular Imaging is the Right Choice

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Molecular imaging technology—specifically whole-body FDG-PET and PET/CT—has long been involved in guiding breast cancer treatment decisions. In fact, staging of breast cancer with FDG-PET has been approved by CMS for reimbursement for quite some time. Today, whole-body PET and PET/CT are fairly widely used and accepted in the staging and clinical management of breast cancer. However, there is currently no uniform clinical utilization of PET and PET/CT in breast cancer. Firm practice guidelines do not exist. In some cases, the technology might be over-used—but more frequently—utilization is much too low.

As 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.”

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 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