A 33-year-old man with a recurrent anaplastic oligodendroglioma (WHO grade III, IDH1-mutant, 1p/19q codeleted). Initial diagnosis occurred at age 26 after resection. After adjuvant therapy with radiotherapy and temozolomide, the patient presented with a growing mass in the right medial frontal lobe in March 2021. Resection revealed a mitotically active tumor, and post-operative management included further cycles of temozolomide. The patient declined additional treatment options after December 2021.
After chemotherapy in December 2021, the tumor showed gradual growth over the next 2.5 years. Thirty three months after last chemotherapy, MRI showed a sudden spontaneous decrease in enhancing tumor size. The area of tumor shrinkage was new after radiation 7 years prior, and was not present at the time of prior chemotherapy, making delayed response or pseudoresponse extremely unlikely. The growth rate of this patient’s tumor prior to regression matched literature on oligodendrogliomas exhibiting slow growth post-treatment cessation.