BIOM-37. INITIAL RADIOGRAPHIC ASSESSMENT OF ADC VALUES IN PEDIATRIC PATIENTS TREATED WITH DAY101 FOR RECURRENT OR PROGRESSIVE LOW-GRADE GLIOMAS (LGGs) HARBORING MEK/ERK PATHWAY ALTERATIONS

Abstract

Abstract BACKGROUND Calculated from a diffusion-weight image (DWI), the apparent diffusion coefficient (ADC) is a quantitative measure that reflects observed net movement of water and correlates to tumor cellularity. We examine the changes in ADC values in patients with LGG treated with dimeric, pan-RAF inhibitor DAY101 (formerly TAK-580/MLN2480). METHODS Focusing on ADC change with treatment, we reviewed historical, baseline, and on-treatment brain MRIs for 9 patients enrolled on our institutional, IRB-approved phase 1 trial of DAY101 in children and young adults with radiographically recurrent or progressive LGG harboring MEK/ERK pathway alterations. De-identified DICOM MRI files were independently reviewed. Time points selected included baseline, first follow-up and best response. The pmod molecular image software package was utilized for data processing of ADC estimates. ADC changes were displayed as a histogram with mean values. Results were based upon a single read paradigm. RESULTS A shift to lower ADC values for solid components of these tumors was observed, reflecting cellularity and organization; while necrosis correlated with a shift toward higher ADC values. DWI results show reduced ADCs in responding patients, with greater percent change in ADC from baseline associated with deeper responses among treated patients. DWI for treated patients with resultant stable disease showed no significant change in ADC values from baseline while a shift toward higher ADC values was evident in treated, progressing tumors. CONCLUSION Preliminary DWI analysis reveals that a reduction in ADC values may correlate with treatment response and a shift toward more normal cellularity in tumors treated with DAY101. This method will be applied to a larger cohort of patients in an ongoing phase 1 trial (NCT03429803) and a planned phase 2 trial.