Positron emission tomography scanning in malignant melanoma - Clinical utility in patients with Stage III disease

BACKGROUND. Several recent studies have demonstrated the low yield of anato mically based computed tomography scans in evaluating Stage III (American J oint Committee on Cancer) patients with malignant melanoma. The purpose of this the METHODS. A prospective evaluation of 106 whole body PET scans obtained afte r injection of 2-fluorine-18, 2-fluoro-2-deoxy-D-glucose (FDG) was performe d in 95 study was to investigate the efficacy and clinical utility of funct ionally based positron emission tomography (PET) scans in the same patient population. patients with clinically evident Stage III lymph node and/or in -transit melanoma. Areas of abnormality on FDG PET scanning were identified visually as foci of increased metabolic activity compared with background, and all positive foci were assessed pathologically. RESULTS. In this patient population, there were 234 areas that were evaluat ed pathologically of which 165 were confirmed histologically to be melanoma . PET scanning identified 144 of the 165 areas of melanoma for a sensitivit y of 87.3%. The 21 areas of melanoma that were missed included 10 microscop ic foci, 9 foci less than 1 cm, and 2 foci greater than 1 cm. There were 39 areas of increased PET activity that were not associated with malignancy f or a 78.6% predictive value of a positive test. Of the 39 false-positive ar eas (false-positive rate of 56.5%), 13 could be attributed to recent surger y, 3 to arthritis, 3 to infection, 2 to superficial phlebitis, 1 to a benig n skin nevus, and 1 to a colonic polyp. Pathologic evaluation of the remain ing false-positive areas failed to reveal a definitive etiology for their i ncreased activity on PET scan. With the application of pertinent clinical i nformation, the predictive Value of a positive PET scan could be improved t o 90.6%, The specificity of PET scanning in this study was only 43.5% becau se very few prophylactic lymph node dissections were performed. Thirty-six of the total 183 abnormal areas (19.7%) on PET scanning proved to be unsusp ected areas of metastatic disease. These findings led to a change in the pl anned clinical management in patients after 16 of the 106 PET scans (15.1%) . CONCLUSIONS. FDG PET scanning can be helpful in managing patients with Stag e III melanoma in whom further surgery is contemplated. Although false-posi tive areas are not uncommon, PET scans did change the management of patient s 15% of the time. PET's inability to identify microscopic disease suggests that it is of limited use in evaluating patients with Stage I-II disease. (C) 2000 American Cancer Society.