Incidence of pseudo-progression in low-grade gliomas treated with radiotherapy.

Abstract

2051 Background: Pseudo-progression (psPD) is a well-known phenomenon in high-grade gliomas (HGG) after treatment with radiotherapy/temozolomide. However the incidence of psPD in low-grade glioma (LGG) after radiotherapy (RT) is unknown. Therefore, we retrospectively investigated the occurrence of psPD in a cohort of low grade glioma patients treated with RT. Methods: All patients with histologically proven LGG treated with RT between 2000 and 2011 were reviewed. MRI scans were reviewed by two independent reviewers before and after RT in periods of 3-6 months until progression leading to the start of a new treatment as judged by the treating physician. Furthermore clinical data including dexamethasone dose and epileptic activity was taken into account. Pseudo-progression was scored when a new enhancing lesion occurred after RT, and this disappeared or remained stable for at least a year without therapy. Results: Seventy-one patients were treated with RT for LGG. Sixty-four patients were deemed eligible for evaluation (3 were lost to follow up and 4 patients were not evaluable, due to a missing scans). The median follow-up was 7 years (range 1- 22 years). The median progression free survival was 3.1 years. The median overall survival time was 5.3 years. Sixty-three patients were evaluable for psPD (1 patient was evaluated for response only, because of gadolinium allergy). psPD was seen in 13 patients (20.6%). In two of these patients epilepsy may have played a role. Pseudo-progression occurred after a median of 10 months in a period of 3 – 78 months. The median duration of psPD was 6 months with a range of 2 – 26 months. It always occurred within the RT fields. The area of the enhancement at the time of pseudo-progression was significantly smaller compared to the area of enhancement during ‘true’ progression (median size 54 mm2 (range 12 – 340 mm2) versus 270 mm2 (range 30 – 3420 mm2), respectively; p = 0.009). Conclusions: psPD occurs frequently in LGG patients treated with RT. This supports the policy to postpone a new line of treatment until further progression is evident, especially when patients have small contrast enhancing lesions in the RT field.