Positron Emission Tomography: Evaluation of the Diagnostic Validity in Metastatic Melanoma

Abstract

The incidence of malignant melanoma is steadily increasing. Since therapeutic success is fairly limited in advanced disease, early detection and diagnosis of metastases still accessible to surgery or radiotherapy determine the prognosis. To assess the diagnostic validity of positron emission tomography (PET) in melanoma patients, we performed a retrospective study comparing the results oi established imaging methods like computed tomogaphy (CT) and PET in 51 melanoma patients. In total 102 organs were affected, harbouring 356 single metastatic lesions. PET and CT, both diagnosed 85 out of lot organ involvements correctly, giving a sensitivity of 94% for CT and 89% for PET. PET missed mainly lung lesions smaller than 8 mm in diameter and cutaneous metastases, 6-10 mm in size. CT frequently failed to diagnose lymph node and bone metastases. CT diagnosed 7 and PET 12 organ involvements false positively. PET is based on metabolic changes, like increased consumption of 18-FDG-Glucose by proliferating tumor cells. Since metabolic changes preceed morphological changes, PET was able to detect lymph node and bone metastases before morphological changes were visible in CT. Although both methods were comparable in regard to sensitivity and specificity, they could not replace each other. We rather think that PET plays a distinct role in oncology. She should be understood as a novel, supplementary method, adding valuable information in the diagnosis of metastatic melanoma.