P01.105 Clinical and imaging features of pseudoprogression in malignant glioma.

Abstract

Background

Pseudoprogression (PP) likely represents a unique phenomenon encountered in high-grade glioma patients within the first six months of combined chemoradiation. As PP mimics recurrent disease, patients may need a tissue biopsy to guide management. We here characterize the clinical and imaging features of biopsy-proven PP, aiming to establish pre-selection criteria for patients requiring biopsy.

Material and Methods

Clinical, radiographic, and histopathological data of patients with malignant glioma and biopsy-proven PP (defined as appearance ≤6 months post radiotherapy (RT) initiation) were retrospectively analyzed. The spatiotemporal pattern of each imaging event/lesion diagnosed as PP defined a region of interest (ROI) and was evaluated via standard T1+C weighted MRI sequences and spatially correlated to the RT treatment plan. Additional non-biopsied ROIs in the same patient with radiographic PP were included in the analysis.

Results

24 patients with biopsy-proven PP were analyzed. All had high-grade gliomas, the vast majority of which were glioblastomas (WHO Grade IV; 87.5%). Tumor pathology revealed MGMT-promoter methylation in 53% (n=9/17), EGFR amplification in 33% (n=7/21) and IDH mutation in 6% (n=1/16). Patient male-to-female ratio was approximately 2:1 and median age at diagnosis was 57.5 years (range: 32 -76 years). All patients underwent RT, 83% had concurrent and adjuvant TMZ-based chemotherapy. Median OS from initial diagnosis was 2.2 years; 12.5% of patients reached 5-year OS. 27 individual radiographic ROIs (n=26 biopsy-proven, n=1 radiographically diagnosed) were analyzed in our cohort. While histopathology of most specimens revealed tissue necrosis, 27% (7/26) showed findings of treatment effect intermixed with foci of solid tumor. Median onset of PP from RT initiation was 2 months (range: 7.5 weeks - 6 months) and associated with new symptoms in over two-thirds of patients, most of which (75%) required steroid treatment.Most patients developed a single ROI (median=1; range: 1 - 5 ROIs) of non-nodular, ring-like enhancing appearance around the tumor resection cavity (RC). Individual ROI size was highly variable (median=3.7 cm ²; range: 0.5 - 32 cm ²; n=16/27) and only one-fourth of ROIs were located at a distance from the RC (range: 1,2 - 6 cm). Accordingly, 100% of ROIs were located within the main radiation field.

Conclusion

PP was enriched in patients with glioblastoma, occurring mostly within 2 months after chemoradiation as a single, ring-like enhancing lesion of variable size. Lesions located to areas exposed to maximum therapeutic radiation dosages, and patients were typically symptomatic requiring anti-edematous therapy and/or surgical debulking. The considerable incidence of lesions with mixed pathology highlights the diagnostic challenge associated with this important neuro-oncological condition.