Preop PET/CT staging for melanoma has high false-positive rate

The use of preoperative PET/CT staging to detect clinically occult metastatic melanoma in patients with sentinel lymph node-positive melanoma has a high false-positive rate and a minimal effect on management, according to a research letter published in JAMA Oncology.

The procedure may be best suited for evaluating treatment response and recurrence, according to researchers. Benjamin Y. Scheier, MD, fellow in the division of hematology and oncology in the University of Michigan's department of internal medicine, and colleagues conducted the study to assess the use of PET/CT in detecting occult metastases in sentinel lymph node (SLN)-positive melanoma.

Clinicians map SLNs as part of the staging of cutaneous melanoma—if a sentinel lymph node biopsy (SLNB) reveals regional metastases, the patient undergoes completion lymph node dissection (LND) with curative intent, according to the study.

The National Comprehensive Cancer Network recommends PET/CT staging prior to LND for prognostic purposes but the procedure is categorized as having low-level evidence. The finding of occult synchronous metastases may preclude the lymph node dissection and present an opportunity for a metastasectomy.

The researchers reviewed data from 46 patients treated at University of Michigan between April 2013 and September 2014 who had PET/CT prior to LND.

One-third had intense uptake distant from the primary tumor and local lymph node basin. Of those, 60 percent had abnormalities biopsied prior to lymph node dissection. One-third of those biopsies (3 of 9) had metastatic melanoma for a 67 percent false-positive rate for PET/CT.

Only 7 percent of the patients in the population had PET/CT findings that identified metastatic melanoma, precluding the lymph node dissection.

There was no association between T stage and N stage regarding whether patients underwent PET/CT imaging.

The data suggest that a significant majority of asymptomatic patients with newly discovered microscopic SLN-positive melanoma do not have synchronous metastases detectable by PET/CT, Scheier and colleagues wrote. “Our review also identified the potential for treatment delays, increased exposure to risk from additional procedures and increased healthcare resource usage that patients incur following detection of asymptomatic abnormalities by preoperative PET/CT. We recommend that PET/CT staging be reevaluated as a category 2B recommendation by the NCCN and its use further evaluated prospectively in a clinical trial.”