FLT-PET in previously untreated patients with low-grade glioma can predict their overall survival

Abstract

BACKGROUND: Low-grade gliomas (LGG) of the brain have an uncertain prognosis, as many of them show continuous growth or upgrade over the course of time. We retrospectively investigated the role of positron emission tomography with 3’-deoxy-3’-[18F]fluorothymidine (FLT-PET) in the prediction of overall survival and event free survival in patients with untreated LGG. No such information is yet available in the literature.

MATERIAL AND METHODS: Forty-one patients with previously untreated LGG underwent 55 FLT-PET investigations during their follow-up because of subjective complaints, objective worsening of clinical conditions, equivocal findings or progression on magnetic resonance imaging. The time interval before referral for neurosurgical or radiation treatment was considered to be event free survival, the interval until death as overall survival, respectively. Standardized uptake values (SUV) were measured, and a 3-point scale of subjective assessment was also applied. ROC analysis was used to define cut-off values. The log rank test was used for comparison of Kaplan-Meier survival curves.

RESULTS: Eight patients (a total of 9 FLT-PET studies performed) died during follow-up. Progression leading to referral to therapy was recorded in 24 patients (a total of 33 FLT-PET studies). With a cut-off value of SUVmean = 0.236, a median overall survival of 1.007 days was observed in the test positive subgroup while median overall survival for the test negative subgroup was not achieved (p = 0.0002), hazard ratio = 17.6. Subjective assessment resulted in hazard ratio 11.5 (p = 0.0001). Only marginal significance (p=0.0562) was achieved in prediction of event free survival.

CONCLUSIONS: Increased FLT uptake in previously untreated patients with LGG is a strong predictor of overall survival. On the other hand, prediction of event free survival was not successful in our cohort, probably because of high prevalence of patients who needed treatment due to symptoms caused by a space-occupying lesion without respect to the proliferative activity of the tumour.