Molecular, Histological, and Clinical Characteristics of Oligodendrogliomas: A Multi-Institutional Retrospective Study

BACKGROUND

Reports suggest that phosphatidylinositol 3-kinase pathway alterations confer increased risk of progression and poor prognosis in oligodendroglioma, IDH-mutant, and 1p/19q-codeleted molecular oligodendrogliomas (mODG). However, factors that affect prognosis in mODG have not been thoroughly studied. In addition, the benefits of adjuvant radiation and temozolomide (TMZ) in mODGs remain to be determined.

OBJECTIVE

To evaluate the role of PIK3CA mutations in mODGs.

METHODS

One hundred seven mODGs (2008-2019) diagnosed at 2 institutions were included. A retrospective review of clinical characteristics, molecular alterations, treatments, and outcomes was performed.

RESULTS

The median age was 37 years, and 61 patients (57%) were male. There were 64 (60%) World Health Organization (WHO) grade 2 and 43 (40%) WHO grade 3 tumors. Eighty-two patients (77%) were stratified as high risk (age 40 years or older and/or subtotal resection per Radiation Treatment Oncology Group-9802). Gross-total resection was achieved in 47 patients (45%). Treatment strategies included observation (n = 15), TMZ (n = 11), radiation (n = 13), radiation/TMZ (n = 62), and others (n = 6). Our results show a benefit of TMZ vs observation in progression-free survival (PFS). No difference in PFS or overall survival (OS) was observed between radiation and radiation/TMZ. PIK3CA mutations were detected in 15 (14%) mODG, and shorter OS was observed in PIK3CA-mutant compared with PIK3CA wild-type mODGs (10.7 years vs 15.1 years, P = .009). WHO grade 3 tumors showed a shorter PFS, but no significant difference in OS was observed between WHO grades.

CONCLUSION

Our findings suggest that mODGs harboring PIK3CA mutations have worse OS. Except for an advantage in PFS with TMZ treatment, adjuvant TMZ, radiation, or a combination of the two showed no significant improvement in OS.

INNV-21. COMPLETE RESPONSE TO ADJUVANT TEPOTINIB IN A PATIENT WITH NEWLY DIAGNOSED DISSEMINATED GLIOBLASTOMA (GBM) HARBORING MET AMPLIFICATION

MET oncogene encodes a receptor-tyrosine-kinase which drives cell proliferation, invasion and angiogenesis in a number of solid cancers including GBM where the incidence of MET amplification is 2-5%. Tepotinib is a highly selective blood-brain-barrier penetrant oral c-MET inhibitor recently FDA approved for MET-exon-14 altered non-small cell lung cancer (NSCLC). Here, we report complete radiographic response to tepotinib in a patient with newly-diagnosed disseminated GBM harboring MET amplification. A 29-years-old male presented with progressive headache. MRI brain showed a large heterogeneously enhancing intraventricular mass with epicenter in the right lateral ventricular trigone and enhancing nodules in bilateral cerebellum. MRI spine showed multifocal enhancement along the periphery of the cervicothoracic spinal cord and cauda equina concerning for leptomeningeal disease. He underwent right temporal lobectomy and subtotal resection of the mass. His KPS was 90 post-surgery due to dizziness. Pathology was consistent with GBM, IDH wild-type, MGMT-unmethylated and MET amplification at 7q31.2. He completed proton craniospinal irradiation at 3600cGy followed by boost to the tumor bed at 2400cGy without concurrent temozolomide (TMZ) due to the large radiation field. He completed two cycles of adjuvant TMZ which was put on hold due to myelosuppression. He subsequently started tepotinib monotherapy at 1000mg daily obtained on a compassionate IND. MRIs after one month of therapy showed resolution of areas of enhancement in the brain and spine. He had grade 1 creatinine elevation and abdominal discomfort and dose was reduced to 500mg daily after two cycles. Nineteen weeks after initiation of tepotinib, his complete response persists, and he remains clinically stable with mild chronic dizziness. Trials of targeted therapy in molecularly-unselected GBM have been largely disappointing, however, this case demonstrates the promise of targeting MET using tepotinib in GBM. A clinical trial of tepotinib in MET-amplified GBM and NSCLC brain metastasis is currently underway at MD Anderson.

PATH-19. MOLECULAR, HISTOLOGIC AND CLINICAL CHARACTERISTICS OF OLIGODENDROGLIOMAS: A MULTI-INSTITUTIONAL RETROSPECTIVE STUDY

In the 2016 WHO classification of CNS tumors, oligodendrogliomas are molecularly defined by IDH1 or IDH2 mutations and 1p/19q co-deletion. Some reports suggest that PI3K pathway alterations may confer increased risk of progression and poor prognosis in oligodendroglioma. However, factors that influence prognosis in molecularly defined oligodendroglioma (mOGD) have not been thoroughly studied. Also, the benefits of adjuvant radiation and temozolomide in mOGDs remain to be determined. 107 mOGDs diagnosed between 2008-2018 at the University of Texas Health Science Center at Houston (n= 39) and MD Anderson Cancer Center (n= 68) were included. A retrospective review of the demographic, clinical, histologic, molecular, and outcomes were performed. Median age at diagnosis was 37 years and 61 (57%) patients were male. There were 64 (60%) WHO Grade 2 and 43 (40%) WHO Grade 3 tumors. Ninety-five (88.8%) tumors were IDH1-mutant and 12 (11.2%) were IDH2-mutant. Eighty-two (77%) patients were stratified as high-risk: older than 40-years and/or subtotal resection (RTOG 9802). Gross-total resection was achieved in 47 (45%) patients. Treatment strategies included observation (n= 15), temozolomide (n= 11), radiation (n= 13), radiation with temozolomide (n= 62) and other (n= 6). Our results show a benefit of temozolomide vs. observation in progression-free survival (PFS). However, no benefit in PFS or overall survival (OS) was observed when comparing radiation vs. radiation with temozolomide. PIK3CA mutations were detected in 15 (14%) cases, and patients with PIK3CA-mutant mOGDs showed worse OS (10.7-years vs 15.1-years, p= 0.009). Patients with WHO Grade 3 tumors had shorter PFS but no significant difference in OS was observed compared to grade 2. Our findings suggest that mOGDs harboring PIK3CA mutations have worse OS. Except for an advantage in PFS in temozolomide treated patients, adjuvant treatment with radiation or the combination of both, showed no significant advantage in terms of OS.

INNV-20. ELEVATED INTRACRANIAL PRESSURE WITHOUT HYDROCEPHALUS IN PATIENTS WITH NEUROFIBROMATOSIS 2

BACKGROUND

Neurofibromatosis 2 is a tumor predisposition syndrome associated with multiple tumors of the central and peripheral nervous systems. Schwannomas and meningiomas are commonly observed. The occurrence of communicating hydrocephalus in this population has been observed clinically but not characterized in the literature.

METHODS

We present a retrospective case series of patients with NF2 and communicating hydrocephalus followed in the Neurofibromatosis clinic at MD Anderson Cancer Center.

RESULTS

We identified 11 patients in our Neurofibromatosis clinic with symptomatic elevation in intracranial pressure (ICP). All patients presented with worsening headaches, while six patients also presented with visual complaints leading to the diagnosis of elevated ICP. Dedicated venous imaging with either MRV or CTV was available for review in five patients. Occlusion or stenosis of the venous system (dural venous sinuses or internal jugular vein) was seen in nine patients. All patients had evidence of plaque-like meningiomas, and two patients had cervical schwannomas. Only one patient had radiographic evidence of obstructive hydrocephalus. All patients were treated for symptomatic elevated ICP with placement of a ventriculoperitoneal (VP) shunt. Three patients received acetazolamide prior to shunting, while one patient received acetazolamide after shunt placement. Seven (7/11) patients had documented improvement or resolution of headache after VP shunt placement. Two (2/6) patients had documented improvement or resolution of visual complaints.

CONCLUSIONS

We present 11 patients with NF2 who developed symptomatic elevation in ICP, ten patients without evidence of obstructive hydrocephalus and one with obstructive hydrocephalus. We hope to raise awareness of this clinical phenomena, previously uncharacterized in the literature. We propose a multifactorial mechanism involving plaque-like meningiomas, venous sinus stenosis, obstruction of cerebral venous outflow and cervical/jugular schwannomas in the development of symptomatic elevated ICP without evidence of obstructive hydrocephalus in patients with NF2.