eIF4A controls translation of estrogen receptor alpha and is a therapeutic target in advanced breast cancer

The majority of human breast cancers are dependent on hormone-stimulated estrogen receptor alpha (ER) and are sensitive to its inhibition. Treatment resistance arises in most advanced cancers due to genetic alterations that promote ligand independent activation of ER itself or ER target genes. Whereas re-targeting of the ER ligand binding domain (LBD) with newer ER antagonists can work in some cases, these drugs are largely ineffective in many genetic backgrounds including ER fusions that lose the LBD or in cancers that hyperactivate ER targets. By identifying the mechanism of ER translation, we herein present an alternative strategy to target ER and difficult to treat ER variants. We find that ER translation is cap-independent and mTOR inhibitor insensitive, but dependent on 5' UTR elements and sensitive to pharmacologic inhibition of the translation initiation factor eIF4A, an mRNA helicase. EIF4A inhibition rapidly reduces expression of ER and short-lived targets of ER such as cyclin D1 and other components of the cyclin D-CDK complex in breast cancer cells. These effects translate into suppression of growth of a variety of ligand-independent breast cancer models including those driven by ER fusion proteins that lack the ligand binding site. The efficacy of eIF4A inhibition is enhanced when it is combined with fulvestrant-an ER degrader. Concomitant inhibition of ER synthesis and induction of its degradation causes synergistic and durable inhibition of ER expression and tumor growth. The clinical importance of these findings is confirmed by results of an early clinical trial ( NCT04092673 ) of the selective eIF4A inhibitor zotatifin in patients with estrogen receptor positive metastatic breast cancer. Multiple clinical responses have been observed on combination therapy including durable regressions. These data suggest that eIF4A inhibition could be a useful new strategy for treating advanced ER+ breast cancer.

Reversion mutations in germline BRCA1/2-mutant tumors reveal a BRCA-mediated phenotype in non-canonical histologies

The association between loss of BRCA1/2 and a homologous recombination deficiency phenotype is lineage dependent. In BRCA-associated cancers such as breast, ovarian, pancreas and prostate, this phenotype confers sensitivity to PARP inhibitors and platinum-therapies. Somatic reversion mutations restoring BRCA1/2 function mediate resistance, and have exclusively been reported in BRCA-associated tumors. In this study, we analyze matched tumor and normal sequencing from 31,927 patients and identify 846 (2.7%) patients with germline BRCA1/2 variants across 43 different cancer types, including 11 with somatic reversion mutations. While nine are in BRCA-associated tumors, we find two reversion mutations in non-BRCA-associated histologies, namely lung and esophagogastric adenocarcinomas. Both were detected following platinum therapy. Whole exome sequencing confirms the homologous recombination deficiency phenotype of these tumors. While reversion mutations arise in all BRCA-associated cancer types, here we show that reversion mutations arising post-platinum in non-BRCA associated histologies, while rare, may indicate BRCA1/2 mediated tumorigenesis.

Abstract OT2-23-01: A Phase 1b/2a, open-label platform study to evaluate mirdametinib in combination with fulvestrant in ER+ metastatic breast cancers harboring MAPK-activating mutations

Background: Approximately 70% of all metastatic breast cancers (MBCs) express estrogen receptor (ER). Hormonal therapies targeting ER are highly active against these cancers and have been remarkably successful in improving outcomes. Unfortunately, resistance to hormonal therapy is nearly universal and over 90% of patients develop resistance to various drugs targeting ER. We have identified mutations in three non-overlapping gene sets that are associated with the hormone-resistant phenotype: (1) ESR1, (2) MAPK pathway, and (3) transcription factors. The finding of mutations that might activate MAPK signaling was particularly striking given the known oncogenic function of this pathway in other cancers and the potential to target this pathway with selective inhibitors. Indeed, in preclinical models, the combination of an allosteric MEK inhibitor with an ER antagonist induced tumor regression in NF1-null, ER+ xenografts that were resistant to antiestrogen monotherapy. These data suggest that MAPK pathway alterations promote resistance to ER-targeted therapies in MBC and lead us to hypothesize that MAPK-targeted therapies will prove highly effective in such patients. However, NF1 (prevalence 6%) is only one of several RAS modulators that are associated with hormone resistance, and KRAS and HRAS mutations were also present in this dataset. Further, receptor tyrosine kinase (RTK) alterations (EGFR amplification and ERBB2 somatic mutations) and mutations in the RAF/MEK kinase cascade (BRAF and MEK1) are present and may comparably confer resistance to hormonal therapy and sensitivity to MAPK pathway inhibition. We hypothesize that MAPK pathway-activated MBCs can be effectively treated using MAPK targeted therapies in combination with hormonal therapy. Patient Accrual:The workflow to enroll patients to clinical trials at MSKCC is automated such that genomic alterations that are deposited on the cBioPortal are matched with appropriate clinical trials using database queries. A recent query of cBioPortal data from ER+ MBC patients treated at MSKCC showed 216 patients harboring actionable alterations in the MAPK pathway. Clinical Trial Design: This investigator-initiated trial being performed in collaboration with SpringWorks Therapeutics is IRB-approved and anticipated to open at MSKCC in August 2021. This is a Phase IB/IIA clinical trial of the allosteric MEK1/2 inhibitor mirdametinib (oral, daily) with the ER antagonist fulvestrant (500mg IM monthly). Inclusion criteria for the study will include ER+ tumor (ASCO-CAP guidelines), MAPK-activating genomic alteration documented by a CLIA-certified NGS assay at any time before the start of treatment, measurable disease, and at least one line of prior endocrine therapy. The feasibility of the combination will be established in a brief safety run-in of full-dose fulvestrant together with mirdametinib with dose de-escalation planned if two Dose Limiting Toxicities (DLT) are observed in the first six patients. This drug combination will then be expanded in three cohorts of patients defined by tumor genotype: (1) RAS activating: NF1 loss, KRAS or HRAS activating mutation, (2) RTK: EGFR amplification or ERBB2 hotspot mutation, (3) RAF/MEK: activating mutation in BRAF, CRAF, or MEK1/2. The primary endpoint for the study will be safety and tolerability of mirdametinib in combination with fulvestrant, and secondary endpoints include Overall Response Rate (ORR), Progression Free Survival (PFS), Clinical Benefit Rate (CBR), and Duration of Response (DOR) for the drug combination in each cohort and for the total study population. Overall survival is not an endpoint of this protocol.

Citation Format: Ezra Y. Rosen, Payal Patel, Nenad Sarapa, Badreddin Edris, Alexia Iasonos, Komal Jhaveri, Pedram Razavi, Mark Robson, Alexander Drilon, Michael F. Berger, David B. Solit, Sarat Chandarlapaty. A Phase 1b/2a, open-label platform study to evaluate mirdametinib in combination with fulvestrant in ER+ metastatic breast cancers harboring MAPK-activating mutations [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-23-01.

A Performance Comparison of Commonly Used Assays to Detect RET Fusions

PURPOSE

Selpercatinib and pralsetinib induce deep and durable responses in patients with advanced RET fusion-positive lung and thyroid cancer. RET fusion testing strategies with rapid and reliable results are critical given recent FDA approval. Here, we assess various clinical assays in a large pan-cancer cohort.

EXPERIMENTAL DESIGN

Tumors underwent DNA-based next-generation sequencing (NGS) with reflex to RNA-based NGS if no mitogenic driver or if a RET structural variant of unknown significance (SVUS) were present. Canonical DNA-level RET fusions and RNA-confirmed RET fusions were considered true fusions. Break-apart FISH and IHC performance were assessed in subgroups.

RESULTS

A total of 171 of 41,869 patients with DNA NGS harbored RET structural variants, including 139 canonical fusions and 32 SVUS. Twelve of 32 (37.5%) SVUS were transcribed into RNA-level fusions, resulting in 151 oncogenic RET fusions. The most common RET fusion-positive tumor types were lung (65.6%) and thyroid (23.2%). The most common partners were KIF5B (45%), CCDC6 (29.1%), and NCOA4 (13.3%). DNA NGS showed 100% (46/46) sensitivity and 99.6% (4,459/4,479) specificity. FISH showed 91.7% (44/48) sensitivity, with lower sensitivity for NCOA4-RET (66.7%, 8/12). A total of 87.5% (7/8) of RET SVUS negative for RNA-level fusions demonstrated rearrangement by FISH. The sensitivity of IHC varied by fusion partner: KIF5B sensitivity was highest (100%, 31/31), followed by CCDC6 (88.9%, 16/18) and NCOA4 (50%, 6/12). Specificity of RET IHC was 82% (73/89).

CONCLUSIONS

Although DNA sequencing has high sensitivity and specificity, RNA sequencing of RET SVUS is necessary. Both FISH and IHC demonstrated lower sensitivity for NCOA4-RET fusions.

Abstract PS11-06: Efficacy and safety of larotrectinib in patients with TRK fusion breast cancer

Introduction: Larotrectinib is a first-in-class, CNS-active, highly selective tropomyosin receptor kinase (TRK) inhibitor approved by the US Food and Drug Administration and European Medicines Agency for the treatment of adult and pediatric patients with tumor agnostic indication for TRK fusion-positive cancer. Larotrectinib produced an objective response rate (ORR) of 79% in 159 patients with TRK fusion-positive cancer across various tumor types (Hong DS et al. Lancet Oncol. 2020). Here we report the efficacy and safety of larotrectinib in the six patients from the NAVIGATE phase II study (NCT02576431) with TRK fusion-positive breast cancer. Methods: Data were obtained for patients with breast cancer harboring a neurotrophic tyrosine receptor kinase (NTRK) gene fusion and treated with larotrectinib in the NAVIGATE study. All patients received 100 mg twice daily on a continuous 28-day schedule. Responses were investigator-assessed per RECIST v1.1 (data cut-off: July 15, 2019). Results: A total of 6 patients with TRK fusion breast cancer were included: 3 with secretory carcinomas, 2 with triple-negative breast cancer (TNBC), and 1 with ER+/HER2− disease. The median age was 49 years (range 32-65). One of the patients with secretory breast cancer was male. All of the secretory cases and 1 TNBC patient harbored an ETV6-NTRK3 fusion, 1 TNBC patient had an LMNA-NTRK1 fusion, and the ER+/HER2− patient had a TPM3-NTRK1 fusion. Four patients had received ≥3 prior systemic therapies. The majority of patients had metastatic disease (n=5); 1 patient had locally advanced disease. The ORR was 83% (95% confidence interval [CI] 36-100) with 5 partial responses, while the ER+/HER2− patient had progressive disease. One of the TNBC patients had brain metastasis with complete resolution of CNS disease while on therapy. The median time to response was 1.7 months (range 0.9-1.9) and the duration of treatment ranged from 0.9 to 12+ months, with 4 patients (3 secretory and 1 TNBC) continuing on therapy at time of data cut. Median duration of response was not reached (95% CI 8.2-NE). Median progression-free survival was 9.1 months (95% CI 1.0-NE). Median overall survival was not reached at a median follow-up of 7.4 months. Four of the 6 patients had worst-grade adverse events (AEs) Grade 1-2; the most common Grade 1-2 AEs were dizziness and nausea. One patient had Grade 3 hepatocellular injury and Grade 4 hepatitis that were related to larotrectinib. There were no discontinuations due to AEs. Conclusion: Larotrectinib demonstrated an ORR in breast cancer patients similar to the ORR reported for larotrectinib across all tumor types, which supports the routine testing for NTRK gene fusions in patients with breast cancer regardless of histology.

Citation Format: Ezra Y. Rosen, Antoine Italiano, Dejan Juric, John A. Reeves, Laura Dima, Nicoletta Brega, Alexander Drilon. Efficacy and safety of larotrectinib in patients with TRK fusion breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS11-06.

Overcoming MET-Dependent Resistance to Selective RET Inhibition in Patients with RET Fusion-Positive Lung Cancer by Combining Selpercatinib with Crizotinib

PURPOSE

The RET proto-oncogene encodes a receptor tyrosine kinase that is activated by gene fusion in 1%-2% of non-small cell lung cancers (NSCLC) and rarely in other cancer types. Selpercatinib is a highly selective RET kinase inhibitor that has recently been approved by the FDA in lung and thyroid cancers with activating RET gene fusions and mutations. Molecular mechanisms of acquired resistance to selpercatinib are poorly understood.

PATIENTS AND METHODS

We studied patients treated on the first-in-human clinical trial of selpercatinib (NCT03157129) who were found to have MET amplification associated with resistance to selpercatinib. We validated MET activation as a targetable mediator of resistance to RET-directed therapy, and combined selpercatinib with the MET/ALK/ROS1 inhibitor crizotinib in a series of single patient protocols (SPP).

RESULTS

MET amplification was identified in posttreatment biopsies in 4 patients with RET fusion-positive NSCLC treated with selpercatinib. In at least one case, MET amplification was clearly evident prior to therapy with selpercatinib. We demonstrate that increased MET expression in RET fusion-positive tumor cells causes resistance to selpercatinib, and this can be overcome by combining selpercatinib with crizotinib. Using SPPs, selpercatinib with crizotinib were given together generating anecdotal evidence of clinical activity and tolerability, with one response lasting 10 months.

CONCLUSIONS

Through the use of SPPs, we were able to offer combination therapy targeting MET-amplified resistance identified on the first-in-human study of selpercatinib. These data suggest that MET dependence is a recurring and potentially targetable mechanism of resistance to selective RET inhibition in advanced NSCLC.

Abstract 16: Landscape and outcome of TRK fusion-positive Cancers

TRK inhibitors achieve marked tumor-agnostic efficacy in TRK fusion-positive cancers and consequently are now an established standard of care. Little is known, however, about the demographics, clinical outcomes, response to alternative standard therapies, or genomic characteristics of TRK fusion-positive cancers. Utilizing a center-wide screening program involving more than 26,000 prospectively sequenced patients, genomic and clinical data from all cases with identified TRK fusions were extracted. An integrated analysis was performed of genomic, therapeutic, and phenomic outcomes. In total, we identified 76 cases with confirmed TRK fusions (0.27% overall prevalence) involving 48 unique rearrangements and 17 distinct cancer types. The presence of a TRK fusion was associated with depletion of concurrent oncogenic drivers (p=4.4E-7) and lower tumor mutation burden (p=4.2E-9), with the exception of colorectal cancer where TRK fusions co-occur with microsatellite instability (MSI-H). Longitudinal profiling in a subset of patients indicated that TRK fusions were present in all sampled timepoints in 82% (14/17) of cases. Progression-free survival on first-line therapy, excluding TRK inhibitors, administered for advanced disease was 9.6 months (95% CI: 4.8-13.2). The best ORR achieved with chemotherapy containing-regimens across all lines of therapy was 63% (95% CI: 41-81). Among 12 patients treated with checkpoint inhibitors, the only response observed was in an MSI-H colorectal patient. TRK fusion-positive cancers can respond to alternative standards of care, although efficacy of immunotherapy in the absence of other predictive biomarkers (MSI-H) appears limited. TRK fusions are present in tumors with simple genomes lacking in concurrent drivers that may partially explain the tumor-agnostic efficacy of TRK inhibitors.

Citation Format: Ezra Y. Rosen, Debra A. Goldman, Jaclyn F. Hechtman, Ryma Benayed, Alison M. Schram, Emiliano Cocco, Sophie Shifman, Yixiao Gong, Ritika Kundra, James P. Solomon, Alberto Bardelli, Maurizio Scaltriti, Alexander Drilon, Alexia Iasonos, Barry S. Taylor, David M. Hyman. Landscape and outcome of TRK fusion-positive Cancers [abstract]. In: Proceedings of the AACR Special Conference on Advancing Precision Medicine Drug Development: Incorporation of Real-World Data and Other Novel Strategies; Jan 9-12, 2020; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_1):Abstract nr 16.

TRK Fusions Are Enriched in Cancers with Uncommon Histologies and the Absence of Canonical Driver Mutations

PURPOSE

TRK inhibitors achieve marked tumor-agnostic efficacy in TRK fusion-positive cancers and consequently are now an established standard of care. Little is known, however, about the demographics, outcomes, response to alternative standard therapies, or genomic characteristics of TRK fusion-positive cancers.

EXPERIMENTAL DESIGN

Utilizing a center-wide screening program involving more than 26,000 prospectively sequenced patients, genomic and clinical data from all cases with TRK fusions were extracted. An integrated analysis was performed of genomic, therapeutic, and phenomic outcomes.

RESULTS

We identified 76 cases with confirmed TRK fusions (0.28% overall prevalence) involving 48 unique rearrangements and 17 cancer types. The presence of a TRK fusion was associated with depletion of concurrent oncogenic drivers (P < 0.001) and lower tumor mutation burden (P < 0.001), with the exception of colorectal cancer where TRK fusions cooccur with microsatellite instability (MSI-H). Longitudinal profiling in a subset of patients indicated that TRK fusions were present in all sampled timepoints in 82% (14/17) of cases. Progression-free survival on first-line therapy, excluding TRK inhibitors, administered for advanced disease was 9.6 months [95% confidence interval (CI), 4.8-13.2]. The best overall response rate achieved with chemotherapy containing-regimens across all lines of therapy was 63% (95% CI, 41-81). Among 12 patients treated with checkpoint inhibitors, a patient with MSI-H colorectal cancer had the only observed response.

CONCLUSIONS

TRK fusion-positive cancers can respond to alternative standards of care, although efficacy of immunotherapy in the absence of other predictive biomarkers (MSI-H) appears limited. TRK fusions are present in tumors with simple genomes lacking in concurrent drivers that may partially explain the tumor-agnostic efficacy of TRK inhibitors.

Real-World Outcomes of an Automated Physician Support System for Genome-Driven Oncology

PURPOSE

Matching patients to investigational therapies requires new tools to support physician decision making. We designed and implemented Precision Insight Support Engine (PRECISE), an automated, just-in-time, clinical-grade informatics platform to identify and dynamically track patients on the basis of molecular and clinical criteria. Real-world use of this tool was analyzed to determine whether PRECISE facilitated enrollment to early-phase, genome-driven trials.

MATERIALS AND METHODS

We analyzed patients who were enrolled in genome-driven, early-phase trials using PRECISE at Memorial Sloan Kettering Cancer Center between April 2014 and January 2018. Primary end point was the proportion of enrolled patients who were successfully identified using PRECISE before enrollment. Secondary end points included time from sequencing and PRECISE identification to enrollment. Reasons for a failure to identify genomically matched patients were also explored.

RESULTS

Data were analyzed from 41 therapeutic trials led by 19 principal investigators. In total, 755 patients were accrued to these studies during the period that PRECISE was used. PRECISE successfully identified 327 patients (43%) before enrollment. Patients were diagnosed with 29 tumor types and harbored alterations in 43 oncogenes, most commonly ERBB2 (21.3%), PIK3CA (14.1%), and BRAF (8.7%). Median time from sequencing to enrollment was 163 days (interquartile range, 66 to 357 days), and from PRECISE identification to enrollment 87 days (interquartile range, 37 to 180 days). Common reasons for failing to identify patients before enrollment included accrual on the basis of molecular alterations that did not match pre-established PRECISE genomic eligibility (140 [33%] of 428) and external sequencing not available for parsing (127 [30%] of 428).

CONCLUSION

PRECISE identified 43% of all patients accrued to a diverse cohort of early-phase, genome-matched studies. Purpose-built informatics platforms represent a novel and potentially effective method for matching patients to molecularly selected studies.

Abstract 1752: BRCA-mediated tumorigenesis is origin and cell-type dependent

BRCA1 and BRCA2 mutations predispose to select cancers, yet the interplay between germline and somatic BRCA alterations in driving tumorigenesis and conferring drug sensitivity remain poorly understood. To determine which tumors are dependent on mutant BRCA, we integrated the prospective clinical sequencing of germline blood and matched tumor specimens from 17,152 advanced cancer patients with zygosity analysis, broader somatic molecular features, and treatment outcomes. Tumor lineage dictated BRCA dependence in cancers of both the 2.7% of carriers with germline pathogenic variants and the 1.8% of patients with somatic loss-of-function mutations in BRCA1 and BRCA2 across 38 affected cancer types. The rate of biallelic inactivation of mutant BRCA1/2 varied by mutational origin and tumor lineage. Consequently, BRCA-mediated phenotypes such as homologous recombination deficiency (HRD) were associated with BRCA1/2 mutations in a cell type- and zygosity-dependent manner. Phenotypic penetrance was greatest in tumors of high-risk cancer types and in tumors with biallelic inactivation of mutant BRCA, independent of its germline or somatic origin. Conversely, heterozygous BRCA mutations in other cancer types conferred no HRD phenotype. These lineage-specific differences among hallmarks of BRCA dependence also predicted differential response to PARP-inhibitor therapy. Collectively, only BRCA mutations in tumors of high BRCA penetrance had a strong selective pressure for somatic biallelic inactivation, conferred dose-dependent somatic phenotypic consequences, and PARP inhibitor sensitivity. In contrast, BRCA1/2-mutant patients with cancers not traditionally associated with BRCA susceptibility generally had tumorigenesis independent of mutant BRCA. Overall, mutant BRCA was a founding pathogenic event on which some tumors depended while in others it was likely a dispensable and biologically neutral passenger mutation unrelated to tumorigenesis. This difference was conditioned by lineage, mutational origin, and zygosity, an understanding of which requires integrated germline and somatic molecular characterization in cancer patients with implications for screening, disease pathogenesis, clinical trial design, and therapy.

Citation Format: Philip Jonsson, Michael L. Cheng, Chaitanya Bandlamudi, Preethi Srinivasan, Shweta S. Chavan, Noah D. Friedman, Ezra Y. Rosen, Allison L. Richards, Nancy Bouvier, S. Duygu Selcuklu, Craig Bielski, Wassim Abida, Ahmet Zehir, Nikolaus Schultz, Mark T. Donoghue, Jose Baselga, Kenneth Offit, Marc Ladanyi, Eileen M. O’Reilly, Howard I. Scher, Zsofia K. Stadler, Mark E. Robson, David M. Hyman, Michael F. Berger, David B. Solit, Barry S. Taylor. BRCA-mediated tumorigenesis is origin and cell-type dependent [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1752.

Tumour lineage shapes BRCA-mediated phenotypes

Mutations in BRCA1 and BRCA2 predispose individuals to certain cancers1-3, and disease-specific screening and preventative strategies have reduced cancer mortality in affected patients4,5. These classical tumour-suppressor genes have tumorigenic effects associated with somatic biallelic inactivation, although haploinsufficiency may also promote the formation and progression of tumours6,7. Moreover, BRCA1/2-mutant tumours are often deficient in the repair of double-stranded DNA breaks by homologous recombination8-13, and consequently exhibit increased therapeutic sensitivity to platinum-containing therapy and inhibitors of poly-(ADP-ribose)-polymerase (PARP)14,15. However, the phenotypic and therapeutic relevance of mutations in BRCA1 or BRCA2 remains poorly defined in most cancer types. Here we show that in the 2.7% and 1.8% of patients with advanced-stage cancer and germline pathogenic or somatic loss-of-function alterations in BRCA1/2, respectively, selective pressure for biallelic inactivation, zygosity-dependent phenotype penetrance, and sensitivity to PARP inhibition were observed only in tumour types associated with increased heritable cancer risk in BRCA1/2 carriers (BRCA-associated cancer types). Conversely, among patients with non-BRCA-associated cancer types, most carriers of these BRCA1/2 mutation types had evidence for tumour pathogenesis that was independent of mutant BRCA1/2. Overall, mutant BRCA is an indispensable founding event for some tumours, but in a considerable proportion of other cancers, it appears to be biologically neutral-a difference predominantly conditioned by tumour lineage-with implications for disease pathogenesis, screening, design of clinical trials and therapeutic decision-making.

Functional genomic analyses identify pathways dysregulated by progranulin deficiency, implicating Wnt signaling

Progranulin (GRN) mutations cause frontotemporal dementia (FTD), but GRN's function in the CNS remains largely unknown. To identify the pathways downstream of GRN, we used weighted gene coexpression network analysis (WGCNA) to develop a systems-level view of transcriptional alterations in a human neural progenitor model of GRN-deficiency. This highlighted key pathways such as apoptosis and ubiquitination in GRN deficient human neurons, while revealing an unexpected major role for the Wnt signaling pathway, which was confirmed by analysis of gene expression data from postmortem FTD brain. Furthermore, we observed that the Wnt receptor Fzd2 was one of only a few genes upregulated at 6 weeks in a GRN knockout mouse, and that FZD2 reduction caused increased apoptosis, while its upregulation promoted neuronal survival in vitro. Together, these in vitro and in vivo data point to an adaptive role for altered Wnt signaling in GRN deficiency-mediated FTD, representing a potential therapeutic target.