IMG-37. A rare glimpse into the 17-year evolution of an untreated IDH-mutant astrocytoma

Abstract World Health Organization (WHO) grade 4 isocitrate-dehydrogenase (IDH) mutant astrocytomas are high grade lesions thought to arise from lower grade tumors that undergo malignant transformation. They are usually found on imaging either incidentally or when the lesions begin to cause symptoms; and treatment is often initiated shortly afterwards with surgical resection followed by chemotherapy and radiation. Here we present a unique case of a 23 year-old male patient at presentation with 17 years of continuous imaging prior to resection of an IDH-mutant astrocytoma due to the patient declining treatment. The tumor growth pattern and radiographic features were analyzed, and a piecewise linear and exponential regression model was developed. Tumor volume was estimated using T2 FLAIR MRI sequences obtained from 2004-2021 and imported into BrainLab Origin Server (Version 3.4) for semi-manual segmentation of FLAIR abnormality. The tumor appeared to have three phases of growth modeled by piecewise linear regression; slow growth of 2.2 cc/year from 2004-2016 (12 years, R2 =0.93), moderate growth of 19.9 cc/year from 2016-2020 (4 years, R2=1), and rapid growth of 216.2 cc/year from 2020-2021 (1 year, R2 =0.74). The increase in the growth rate correlates with initial contrast enhancement of the tumor in 2016, which was also associated with suspected partial seizures and memory problems, indicating possible malignant transformation. The entire duration of tumor growth from initial diagnosis to resection was modeled with an exponential regression with growth rate constant of k=0.0033 per day and doubling time of 212 days (R2=0.93). The patient eventually underwent gross total resection and declined adjuvant therapy. He had 16.8 months of progression-free survival and an overall survival of 18.6 months.