Purpose: Positron emission tomography (PET) scanning is an efficient and well-known diagnostic tool in various malignant disorders. However, the utility of PET as a clinical routine screening procedure for the detection of subclinical metastases in stage III melanoma patients has not yet been established.
Methods: Thirty-three patients with cutaneous malignant melanoma and subclinical lymph node metastases diagnosed by sentinel node biopsy (SNB) were submitted to( 18)F-fluoro-2-deoxy-D: -glucose (FDG) whole-body PET scanning within 100 days after SNB and wide local excision. Before PET scanning, patients were screened conventionally and found to be without evidence of further dissemination. Positive PET scan findings were evaluated by computed tomography scanning, magnetic resonance imaging and ultrasonography. Biopsy was performed whenever possible. The median follow-up was 15 months (range 6-39 months).
Results: Nine patients (27%) had a positive PET scan performed after SNB and WLE. On verification, four cases (12%) were found to be true positive for melanoma metastasis and were thus upgraded from stage III to stage IV. Furthermore, one patient (3%) had another primary malignancy (prostate carcinoma), and two (6%) were found to have non-malignant lesions. Two PET-positive patients (6%) refused further investigations. In one case (3%) the PET scan was false negative. Twenty-three (69%) PET scans were true negative.
Conclusion: In a number of stage III melanoma patients with positive SNB, postoperative whole-body FDG-PET scanning revealed further melanoma dissemination not found by conventional screening methods and thus identified these cases as stage IV. Relevant therapy can accordingly be instituted earlier on the basis of FDG-PET scanning.