PEM: An Additional Arrow In the Breast Imaging Quiver

Many physicians and patients cast staging breast MRI as an imperfect exam. From the physician’s perspective, the exam generates thousands of difficult-to-interpret images. False-positive findings are not uncommon. The exam may be difficult for some women to tolerate, and for those with renal insufficiency or claustrophobia, it may be impossible.

Enter positron emission mammography, a focused molecular imaging technique that may provide a tolerable, and clinically superior, alternative particularly for lumpectomy candidates. Despite these positives, PEM is not without pain points.

The Center for Breast Care at Boca Raton Community Hospital in Florida. has used PEM for seven years as an alternative to breast MRI for lumpectomy candidates as well as restaging of patients with a remote history of breast cancer. Similarly, Swedish Cancer Institute in Seattle, uses PEM to evaluate lumpectomy candidates, particularly among women unable to undergo MRI, for multifocal or multicentric disease that might prompt a complete mastectomy rather than a lumpectomy, explains Carolyn L. Wang, MD.

Studies comparing PEM and breast MRI among lumpectomy candidates have showed comparable sensitivity and improved specificity with the molecular technique. “False positives, one of the most annoying aspects of breast MRI, are reduced,” confirms Kathy Schilling, MD, medical director of imaging and intervention at the Center for Breast Care. The false-positive conundrum is compounded among women with claustrophobia as completed exams may be suboptimal and difficult to interpret. 

Breast MRI is hampered by other challenges as well; benign findings often enhance, which prompts additional short-term followup as well as patient anxiety, lost productivity among physicians and increased costs. PEM generates 48 to 60 tomographic images, making for a simpler interpretation.

PEM bests MRI on the patient-friendliness front as well. In the ACRIN 6666 trial, some 58 percent of 1,215 women with elevated breast cancer risk who could undergo breast MR underwent the exam; the remainder refused. Claustrophobia topped the list of reasons for refusal with 25 percent of women citing the condition. “PEM,” says Schilling, “is a great alternative.”

During the 40-minute PEM exam, the technologist remains with the patient, which provides an opportunity for the technologist to answer questions and interact with women who are anxious about their diagnosis.

PEM pain points

Practices considering the transition from breast MRI to PEM for women with appropriate indications need to anticipate potential stumbling blocks, which range from volume to personnel to informatics and referring physician relationships.

“If the practice is primarily MRI-driven, it will be shifting patients from MRI to PEM, so MRI volume will be cut. However, patient satisfaction is likely to improve,” offers Schilling.

Satisfaction hinges, to a degree, on staff. Swedish Cancer Institute employs technologists cross-trained in mammography and nuclear medicine to perform PEM exams. “They have to know how to position the breast properly, which can be difficult. We try to mimic mammography positions,” explains Wang. Thus, a center launching a PEM service might need to cross-train technologists. 

At Swedish, PEM studies are managed in a nuclear medicine PACS and read on a dedicated viewer side-by-side the PACS workstation.

The PEM-based focused molecular imaging model has spurred nuclear medicine physicians at Swedish to cultivate relationships with other physicians. Mammographers may be called upon to help troubleshoot abnormal findings as they provide the dedicated breast imaging expertise. The nuclear medicine department asked breast imaging subspecialty-trained radiologists to provide training for nuclear medicine physicians and PET/CT radiologists in breast biopsy as it launched a PEM-guided biopsy option, which is used in cases of a focal suspicious abnormality on PEM that cannot be found on mammography or ultrasound.

Smaller nuclear medicine groups that want to build a PEM program and lack in-house resources may need to build partnerships with other practices, says Wang.

Another key stakeholder group is referring physicians. Wang and her nuclear medicine colleagues attend all breast tumor boards and share PET/CT and PEM images at the meetings. This helps radiation oncologists and surgeons understand the value of the modality. Physician buy-in is critical, says Wang. “They often have to call payors regarding the exam, and they are more likely to order it and invest the time in the call when they see how useful it is.”

The group also reviews current research and shares it with physicians. For example, at The University of Chicago researchers aim to determine if PEM can evaluate neoadjuvant chemotherapy treatment response earlier in the cycle than MRI. Boston University researchers have devised a study comparing PEM with mammography for the detection of malignant lesions among women with dense breasts. 

“This is going to be the future,” predicts Schilling. “[Using PEM] we’ll be able to see how [malignant] cells are functioning differently than normal cells.”