AJR: PEM FDG uptake values provide prognostic clues

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Mediolateral oblique PEM image of a 68-year-old woman, curved arrows indicate known cancer

18F-FDG uptake values measured by positron emission mammography (PEM) correlated with prognostic indicators that predict breast cancer survival and inform clinical management, including receptor status, tumor histology and tumor grade, according to a study published in the August issue of American Journal of Roentgenology.

Previous studies of whole-body PET have suggested that ER- tumors have a significantly higher maximum standard uptake value (SUV) than ER+ tumors. Similarly, studies have suggested that PR- tumors have a significantly higher maximum SUV than PR+ tumors.

Researchers designed a retrospective study to examine possible correlation between FDG values on PEM and ER, PR and HER2 status, tumor histology, tumor grade and tumor size. The researchers also compared maximum uptake value on PEM and whole-body PET/CT to determine any links between those values.

Carolyn L. Wang, MD, of Swedish Cancer Institute and the department of radiology at University of Washington, both in Seattle, and colleagues reviewed the records of 98 newly diagnosed breast cancer patients with 100 lesions referred for PEM between June 2007 and September 2009.

Two radiologists blinded to the histologic profile of the lesions independently reviewed PEM and PET/CT lesions.

ER- tumors and PR- tumors had significantly higher mean lesion-to-background ratio than did respective receptor-positive tumors, reported Wang et al. Triple negative (ER-, PR- and HER2- tumors) had statistically higher mean lesion-to-background ratios than ER+ PR+ HER2- tumors. The researchers found infiltrating ductal cancers had significantly higher PEM uptake values than infiltrating lobular carcinomas, and tumors with higher histologic grade had higher PEM uptake values than those of lower grade.

There was a moderately high correlation between PEM and PET/CT uptake values in the 99 lesions with PET/CT data.

Wang and colleagues confirmed the importance of their findings. Triple negative tumors have poorer prognoses, they wrote. There is no known targeted therapy and they have a higher risk for early relapse, but are sensitive to primary chemotherapy. “Evaluating early response to neoadjuvant chemotherapy could be accomplished in earlier stage disease using PEM, because of its superior spatial resolution relative to whole-body scanners,” wrote Wang et al.

The researchers reviewed other PEM applications, noting that it could play a role in the initial staging of breast cancer and in defining preoperative disease extended to the ipsilateral breast.

They also suggested that lesion-to-background ratios and SUVs may be connected to other high-risk markers that have not yet been determined. Wang and colleagues noted that additional research and more outcomes data are required to determine the clinical significance of lesion-to-background ratio and SUV.

Another future research need, continued the researchers, is to determine whether there might be a possible role for PEM to determine treatment response.

Wang et al noted several limitations to the study, including its retrospective nature, focusing on relatively large tumors and relatively small sample size. “Future studies are required to determine whether these results will hold in smaller tumors, which may be a strength of PEM,” they wrote.

The researchers reinforced their findings, emphasizing that FDG uptake with PEM appears to correlate with known prognostic indicators.