FDG PET in early stage cutaneous malignant melanoma

Fluorodeoxyglucose positron emission tomography (FDG PET) is not recommended in early stage melanoma; however, a significant number of cases are referred to our institution for FDG PET. We refer to early stage disease as American Joint Committee on Cancer (AJCC) stage I and II, which includes all cases without metastases. A retrospective review was undertaken to determine the clinical utility of FDG PET in this patient group.

A retrospective study of FDG scans on all patients presenting to the WA PET Centre with early stage melanoma over a 5½ year period was undertaken. The positivity rate of the initial study for detection of malignant melanoma was determined. In patients with an initially negative FDG PET, the time from initial diagnosis to a positive surveillance study was determined. Both the initial positivity rate and time to a positive study were correlated with Breslow staging.

Three hundred twenty-two patients were included in the study, of which 74 had initial positive FDG PET scans (23%). Adequate follow-up was available in 51 patients with the PET result confirmed as true positive in 37 (positive predictive value 73%). One hundred eight of 248 patients initially negative had follow-up scans during the follow-up period, of which 48 became positive. The 73% of recurrences were over 12 months post-diagnosis. No correlation with Breslow thickness was demonstrated.

Despite FDG PET not being recommended for early cutaneous malignant melanoma, 27% of melanoma cases referred for FDG PET during the study period were AJCC stage I or II. Our results suggest FDG PET in early stage melanoma demonstrates occult disease in 17% of cases.