493P - The usefulness of pre-radiotherapy MRI in assessing pseudo-progression in patients with glioblastoma included in first-line clinical trials

Background

Advances in the first-line treatment of glioblastoma (GBM) are limited by the lack of correlation between early phase studies, which often use PFS as an endpoint, and subsequent clinical trials (CT). A limitation of using PFS as a surrogate endpoint for OS in GBM is the phenomenon of pseudo-progression. However, GBM has a mean volumetric doubling time of 21 - 30 days, so true progression or new lesions may occur during the surgery-radiotherapy interval, with the incidence ranging from 19 to 75%. Our objective was to analyze the incidence of changes between post-surgical and pre-RDT MRIs and to demonstrate that pre-RDT MRI can improve PFS assessment in patients (pts) treated in CT.

Methods

A total of 32 pts diagnosed with GBM were enrolled in this retrospective analysis. All these pts were included in CT that required a pre-RDT MRI to assess the lack of bleeding or infection. Clinical factors, such as tumor multifocality, the extent of surgical resection, and residual tumor in the postsurgical, pre-RDT, and post-RDT MRI were analyzed.

Results

All patients underwent post-surgical (<72h) and pre-RDT MRIs with a median of 5 days before radiotherapy (RDT) (the median interval between surgery and RDT was 43 days). The extent of resection was complete in 34%, partial in 59%, and 6% biopsy only. Multifocality was identified in 16% of pts on baseline MRI findings. Considering the pre-RDT MRI, 28% of pts exhibited stable results, 50% had progression within the resection area and 22% had additional lessons, marking a 28.5% increase in multifocal tumors that initially presented as solitary lesions. The presence of progression in the pre-RDT MRI was an adverse prognostic factor but it was also associated with a greater risk of being considered to have progressive disease in the first 6 months after diagnosis. The median OS was 10 vs 15 months (p= 0,3) in pts with and without provisional tumor growth, respectively.

Conclusions

While many clinical trials require conducting a pre-RDT MRI, to assess the lack of exclusion criteria, using the full diagnostic and prognostic information could be useful to determine PFS and at least in some cases optimize RDT plans.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

O. Mirallas: Financial Interests, Personal, Invited Speaker: ROVI; Financial Interests, Institutional, Writing Engagement: Roche, Merck; Other, Travel Expenses: Kyowa Kirin, Almirall; Other, Travel Expenses and Conference Fee: Sanofi; Other, Travel expenses: Recordati. M. Gonzalez Rodriguez: Financial Interests, Personal, Invited Speaker: MSD, Pfiser, Roche, AstraZeneca; Financial Interests, Personal, Other, Review clinical cases: Bayer; Financial Interests, Personal, Other, Travel: Ipsen. X. Maldonado: Financial Interests, Personal, Invited Speaker: Bayer, Ipsen; Financial Interests, Personal, Other, Travel grant: Cassen Recordatti. M. Vieito: Financial Interests, Personal, Invited Speaker: Novocure; Financial Interests, Personal, Other, Steering committee member: BMS; Non-Financial Interests, Principal Investigator: Roche, BMS, Taiho, Hutchinson Pharma, Novartis, Mundipharma, Enterome, Debiopharm. All other authors have declared no conflicts of interest.