Lung lesions with hypermetabolic activity on PET not necessarily benign

NEW YORK (Reuters Health) – Positron emission tomography using F-18 fluorodeoxyglucose (FDG-PET) is not always adequate to diagnose a benign lung lesion, University of Pennsylvania researchers warn, especially in a patient with suspected recurrent lung cancer or metastatic extrapulmonary cancer.

Dr. Abass Alavi and colleagues note in the December issue of Chest that based on previous studies, "some authors have suggested that PET evaluation demonstrating hypermetabolic activity in the location of the lesion in question, with a SUR [standardized uptake ratio] of <2.5, is adequate to diagnose a benign nodule," when the lesion is 1.2 cm or larger.

Suspicious that their institution's false-negative and false-positive rates were higher than those in published series, Dr. Alavi's group retrospectively reviewed patients who had undergone FDG-PET over a 2-year period for evaluation of a new lung nodule or mass. Definitive pathology or follow-up imaging established a diagnosis of malignancy or a benign condition in 71 of the 196 cases.

In comparison with the findings on follow-up, FDG-PET had been false-negative in five cases and false-positive in seven, the research team found. Thus, overall its sensitivity was 88% and its specificity was 75%.

"The five false-negative cases occurred when the lesion in question was at least 1.2 to 1.5 cm in size," Dr. Alavi's team states. "In all five false-negative cases, PET failed to show any hypermetabolic uptake, so an SUR value could not be calculated." Histology showed that four of the false-negative lesions were adenocarcinoma or squamous cell carcinoma, which typically are hypermetabolic tumors, the investigators point out.

They found that FDG-PET was most accurate in patients without a history of cancer. Of the 94 such patients whose records were reviewed, a diagnosis was established for 37. FDG-PET results were false-positive in three cases and false-negative in one, for a sensitivity of 95% and a specificity of 82%. The corresponding figures were 92% and 63% for patients with a history of extrapulmonary primary cancer and 70% and 67% for those with a previous primary lung cancer.

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