Interpretation of Positron Emission Mammography: Feature Analysis and Rates of Malignancy

OBJECTIVE. The purpose of our study was to define and illustrate standard terminology for describing findings on positron emission mammography (PEM) and provide associated rates of malignancy. SUBJECTS AND METHODS. Three hundred eighty-eight women with newly-diagnosed breast cancer anticipating breast-conserving surgery completed a multicenter trial comparing PEM to MRI in assessment of disease extent. Morphologic terminology to describe PEM findings was patterned on BI-RADS for MRI, and investigators were trained in the PEM lexicon. PEM imaging features of known malignancies and additional PEM lesions were recorded and correlated with outcome. The reference standard was biopsy or at least a 6-month follow-up. RESULTS. Of 166 additional lesions on PEM, 54 (33%) proved malignant, with median invasive tumor size 8 mm (range, 2-60 mm). Among 43 round or oval masses, 16 (37%) were malignant, compared with 16 of 21 (76%) of lobulated or irregular masses (p = 0.003). Among 14 findings of focal or regional nonmass uptake, two (14%) were malignant compared with four of 12 (33%) findings of linear-ductal or segmental uptake (p = 0.350). Malignancy rates for BI-RADS-type final assessments were category 2, one of 31 (3.2%); 3, three of 32 (9.4%); 4a, four of 18 (22%); 4b, nine of 33 (27%); 4c, 15 of 24 (63%); and 5, 22 of 28 (79%). On the basis of modeling, irregular or lobulated morphology was the strongest predictor of malignancy, followed by lesion laterality (i.e., ipsilateral to known cancer) then increasing semiquantitative (18)F-FDG uptake. CONCLUSION. Use of standardized terminology to report PEM findings will facilitate effective communication of results and consistent management. A probably benign category 3 assessment carried a substantial rate of malignancy for lesions seen on PEM, and biopsy may be more appropriate than follow-up.