Fluorodeoxyglucose positron emission tomography fails to detect distant metastases at initial staging of melanoma patients with metastatic involvement of sentinel lymph node.

BACKGROUND: Positron emission tomography (PET) using fluorodeoxyglucose (FDG) has proven to be more sensitive and accurate than other imaging modalities for the detection of distant metastases in patients with melanoma. Sentinel lymph node (SLN) status is the most important prognostic factor in melanoma patients with no evidence of distant metastasis.

OBJECTIVES: To assess the rate of distant metastases in patients with a positive SLN biopsy (SLNB).

METHODS: Forty-six consecutive patients with a positive SLNB underwent PET or PET-computed tomography within 6 weeks of the SLNB procedure. The patients did not present any clinical sign of nodal involvement or of distant metastasis. PET findings were classified as positive, negative or nonconclusive.

RESULTS: No patient had a positive PET scan for distant metastasis. Six patients (13%) had a nonconclusive PET scan; none of them presented distant metastasis within 12 months. Forty patients (87%) had a negative PET scan; among them five (12%) presented with distant metastasis within 12 months.

CONCLUSIONS: Fluorodeoxyglucose positron emission tomography failed to detect distant metastases at initial staging in patients with a positive SLNB, even in patients who presented with distant metastases within 12 months after the FDG PET scan. These results could be explained by the low prevalence of macroscopic metastatic disease at this stage and by the important delay between the onset of the spread of microscopic metastatic disease and the identification by PET scan of macroscopic metastatic disease.