Initial staging of malignant melanoma by positron emission tomography and sentinel node biopsy

By a retrospective study and literature review we aimed to evaluate the accuracy of Sentinel Node Biopsy (SNB) and F-18-fluorodeoxyglucose positron emission tomography (PET) for early detection of lymph node metastases.

Every patient presenting with a malignant melanoma without clinical lymph node involvement and a Breslow index over 1 mm or a recurrence was subjected to a preoperative PET scan and a sentinel node biopsy. Over a period of 10 months, 5 patients were included. They were submitted to conventional staging techniques, PET and SNB.

In none of the patients the PET scan showed signs of lymph node involvement or distant metastases. However, two patients, both with a Breslow index of 1.4, had micrometastases in the sentinel node.

Already in this small group of patients, PET scanning missed two metastases (40%). This is confirmed by several recent publications, stating that the resolution of positron emission tomography is about 5 mm and thus insufficient to detect micrometastases. Several larger series showed a sensitivity of PET to detect lymph node involvement of 15-50%. Therefore we conclude that PET is of limited use in these patients without palpable lymph nodes. Sentinel node biopsy however proves to be a useful tool and should be considered in the initial staging of malignant melanoma without palpable lymph node or distant metastases.