P04.09 Frequent inactivating mutations of PBRM1 in meningioma with papillary features

BACKGROUND

Papillary meningiomas (PM) are rare WHO grade III tumors that are associated with frequent recurrences and metastatic disease in spite of surgery and radiation. Due to their low incidence and scarcity of tumor tissues available for genomic analyses, the genetic alterations associated with PM remain unclear.

MATERIAL AND METHODS

We mined data collected as part of our clinical comprehensive genomic profiling (CGP) initiative which has to date analyzed 8 PM (>50% papillary morphology) and 22 meningiomas with focal papillary features (10–50%) amongst over 500 additional meningiomas of other subtypes. The samples were analyzed in a CAP/CLIA-accredited laboratory (Foundation Medicine, Cambridge, MA). GCP was performed on hybridization-captured, adaptor ligation-based libraries to a mean coverage depth of >650x for 236 or 315 genes plus the introns from 19 or 28 genes frequently involved in cancer.

RESULTS

In our cohort of 8 PMs, we identified three cases with inactivation of PBRM1; two cases with a truncating mutation in PBRM1 and one with homozygous deletion of PBRM1. Of the 22 meningiomas with only focal papillary features, 8 cases were PBRM1-mutant. Thus, 11 of 30 cases (36.7%) with at least focal (>10%) papillary morphology had inactivation of PBRM1.In the entire cohort of 562 meningiomas, we identified five additional cases with inactivating alterations in PBRM1 that did not display overt papillary morphology in the H&E sections available for analysis. Thus, 11 of 16 PBRM1-mutant cases (69%) occurred in meningioma with papillary histologic features as opposed to 19 of 546 wild-type cases (3.5%), supporting a significant association between papillary features and PBRM1 mutation (p<0.0001). The majority of PBRM1-mutant meningiomas occurred in female patients (n=10/16, 62.5%), and median age was 51 years. Most cases were located supratentorially (n=10).

CONCLUSION

We identified the tumor suppressor gene PBRM1 as a recurrently altered gene in meningiomas with papillary histomorphology. Further investigational studies are needed to assess outcomes of PBRM1-mutant meningioma and to determine whether mutation is an independent negative prognostic biomarker.

Abstract OT2-06-01: Phase I/II study of T-DM1 alone versus T-DM1 and metronomic temozolomide in secondary prevention of HER2-Positive breast cancer brain metastases following stereotactic radiosurgery

Background: Brain metastases occur in up to 25-40% of HER2+ breast cancer patients. Standard treatment is limited to surgery or stereotactic radiosurgery (SRS) and/or whole brain radiation therapy (WBRT), with high levels of recurrence or progression, limiting survival and quality of life in most patients. Our group has demonstrated that low doses of temozolomide (TMZ) administered in a prophylactic, metronomic fashion can significantly prevent development of brain metastases in murine models of breast cancer. Based on these findings, we propose a secondary-prevention clinical trial.

Trial Design: Phase I/II open label study. Phase I will follow a standard 3+3 design: T-DM1 3.6 mg/kg IV every 21 days plus TMZ 30, 40 or 50 mg/m2 daily. Phase II: randomization T-DM1 3.6 mg/kg versus T-DM1 3.6mg/kg plus TMZ at recommended phase 2 dose (RP2D). Patients will undergo radiology guided lumbar puncture at baseline and after 6 weeks of treatment (C3D1) for correlative studies, brain MRI, systemic restaging CTs, and questionnaires for evaluation of symptoms and quality of life (MDASI-BT and PROMIS®) every 6 weeks.

Eligibility: HER2+ breast cancer with ≤3 brain metastases, treated with SRS and/or resection ≤6 weeks before enrollment, no leptomeningeal metastases, no previous WBRT, able to complete brain MRI with contrast evaluations, willing to undergo lumbar puncture, ECOG ≤2 and adequate organ and marrow function. HBV, HCV or HIV-positive patients are ineligible.

Specific Aims: Phase I: to identify the maximum tolerated dose (MTD) of TMZ combined with T-DM1. Phase II: to determine if the combination regimen of T-DM1 and TMZ improves the recurrence-free incidence from distant new brain metastases at one year as compared to T-DM1 alone. Biomarkers, including cell free DNA sequencing from CSF, serum and tumor block, serum markers for neuroinflammation, and patient reported outcomes, will be analyzed in an exploratory fashion.

Statistical Methods: Phase I, MTD will be identified based on the dose level at which 0 or 1 patient in 6 has a DLT. Phase II, to test whether TMZ will increase RFS from 50% to 65% at 12 months. RFS Kaplan-Meier curves will be created for each of the randomized arms and compared using a one-tailed log-rank test, with a one-sided 0.10 significance level of interest to be detected. Patients will be stratified for number of brain lesions and status of systemic metastases (controlled or not).

Target Accrual: 49 evaluable patients per arm (total 98), plus 9 to 18 patients during phase I. Trial will open in Summer 2017, at NIH in Bethesda, MD.

Contact Information: Principal Investigator: Alexandra S Zimmer, MD alexandra.zimmer@nih.gov

Citation Format: Zimmer AS, Gril B, Steinberg S, Smart D, Gilbert M, Armstrong T, Xiao L, Houston N, Biassou N, Brastianos P, Carter S, Lyden DC, Lipkowitz S, Steeg P. Phase I/II study of T-DM1 alone versus T-DM1 and metronomic temozolomide in secondary prevention of HER2-Positive breast cancer brain metastases following stereotactic radiosurgery [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-06-01.