Prognostic relevance of FDG PET in patients with neurofibromatosis type-1 and malignant peripheral nerve sheath tumours

Purpose: In patients with neurofibromatosis type-1 (NF1) and malignant peripheral nerve sheath tumours (MPNSTs), survival rates are low and time to death is often less than 2 years. However, there are patients with a more favourable prognosis who develop metastases rather late or not at all. Since histopathology and tumour grading are not well correlated with prognosis, we aimed to evaluate the potential of F-18-fluorodeoxyglucose positron emission tomography (FDG PET) for prediction of patient outcome in MPNST. Methods: FDG PET was performed in 16 patients with NF1 and MPNSTs. Standardised uptake values (SUVs) were calculated for each tumour and correlated to tumour grade and patient outcome in terms of survival or death. Results: Three patients with tumour grade II had an SUV < 3. None of these patients developed metastases or died during a follow-up of 41-62 months. Thirteen patients with tumour grades II and III had an SUV > 3. Only one of these patients is still alive after 20 months; the remaining 12 died within 4-33 months. SUV predicted long-term survival with an accuracy of 94%, compared with 69% for tumour grade. In Kaplan-Meier survival analysis, patients with an SUV > 3 had a significantly shorter mean survival time, 13 months, than patients with an SUV < 3, in whom the mean survival time was 52 months. Tumour grading did not reveal differences in survival time (15 vs 12 months). Conclusion: Tumour SUV obtained by FDG PET was a significant parameter for prediction of survival in NF1 patients with MPNSTs while histopathological tumour grading did not predict outcome.