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Purpose: Women have traditionally been underrepresented in MD and MD-PhD training programs. Here, we describe the changing demographics of an MD-PhD Program over three distinct time intervals. Methods: We designed a 64-question survey and sent it to 47 graduates of the McGill University MD-PhD program in Montréal, Québec, Canada, since its inception in 1985. We also sent a 23-question survey to the 24 students of the program in 2021. The surveys included questions related to demographics, physician-scientist training, research metrics, as well as academic and personal considerations.Results: We collected responses from August 2020 to August 2021 and grouped them into three intervals based on respondent graduation year: 1995–2005 (n = 17), 2006–2020 (n = 23) and current students (n = 24). Total response rate was 90.1% (n = 64/71). We found that there are more women currently in the program compared to the 1995–2005 cohort (41.7% increase, p

Single-cell technologies have enabled the characterization of the tumour microenvironment at unprecedented depth and have revealed vast cellular diversity among tumour cells and their niche. Anti-tumour immunity relies on cell–cell relationships within the tumour microenvironment1,2, yet many single-cell studies lack spatial context and rely on dissociated tissues3. Here we applied imaging mass cytometry to characterize the immunological landscape of 139 high-grade glioma and 46 brain metastasis tumours from patients. Single-cell analysis of more than 1.1 million cells across 389 high-dimensional histopathology images enabled the spatial resolution of immune lineages and activation states, revealing differences in immune landscapes between primary tumours and brain metastases from diverse solid cancers. These analyses revealed cellular neighbourhoods associated with survival in patients with glioblastoma, which we leveraged to identify a unique population of myeloperoxidase (MPO)-positive macrophages associated with long-term survival. Our findings provide insight into the biology of primary and metastatic brain tumours, reinforcing the value of integrating spatial resolution to single-cell datasets to dissect the microenvironmental contexture of cancer.

Supplementary legends and methods

FIGURE S1: LY3009120 is an effective inhibitor of BRAF class II mutant melanoma cells. FIGURE S2: Bioinformatic characterization of PDX models. FIGURE S3: Inhibitory effects of BRAF and MEK inhibitors in melanoma cells. FIGURE S4: Representative images from cell growth clonogenic assays. FIGURE S5: Encorafenib and binimetinib are an effective combination for class II BRAF mutant melanoma. FIGURE S6: Dual MAPK inhibition slows progression of class II BRAF mutant melanoma brain metastases.

Purpose:Dual MAPK pathway inhibition (dMAPKi) with BRAF and MEK inhibitors improves survival in BRAF V600E/K mutant melanoma, but the efficacy of dMAPKi in non-V600 BRAF mutant tumors is poorly understood. We sought to characterize the responsiveness of class II (enhanced kinase activity, dimerization dependent) BRAF mutant melanoma to dMAPKi.Experimental Design:Tumors from patients with BRAF wild-type (WT), V600E (class I), and L597S (class II) metastatic melanoma were used to generate patient-derived xenografts (PDX). We assembled a panel of melanoma cell lines with class IIa (activation segment) or IIb (p-loop) mutations and compared these with WT or V600E/K BRAF mutant cells. Cell lines and PDXs were treated with BRAFi (vemurafenib, dabrafenib, encorafenib, and LY3009120), MEKi (cobimetinib, trametinib, and binimetinib), or the combination. We identified 2 patients with BRAF L597S metastatic melanoma who were treated with dMAPKi.Results:BRAFi impaired MAPK signaling and cell growth in class I and II BRAF mutant cells. dMAPKi was more effective than either single MAPKi at inhibiting cell growth in all class II BRAF mutant cells tested. dMAPKi caused tumor regression in two melanoma PDXs with class II BRAF mutations and prolonged survival of mice with class II BRAF mutant melanoma brain metastases. Two patients with BRAF L597S mutant melanoma clinically responded to dMAPKi.Conclusions:Class II BRAF mutant melanoma is growth inhibited by dMAPKi. Responses to dMAPKi have been observed in 2 patients with class II BRAF mutant melanoma. These data provide rationale for clinical investigation of dMAPKi in patients with class II BRAF mutant metastatic melanoma.See related commentary by Johnson and Dahlman, p. 6107.

We updated our data set, please use thenew version(md5:ece00981be0f2616c1c0a57d10f3176e). All data supporting the findings of the publication "Single-cell spatial immune landscapeof primary and metastatic brain tumours", including masks of high-dimension tif images, single-cell segmentation, single-cell cell types, and patient data. The code used to produce the results of this study is available at https://github.com/walsh-quail-labs/IMC_Brain. Raw primary imaging data can be obtained from the authors directly upon reasonable request. Glioma channel index names: Channel Name Channel Index CD117 1 CD11c 2 CD14 3 CD163 4 CD16 5 CD20 6 CD31 7 CD3 8 CD4 9 CD68 10 CD8 11 CD94 12 DNA1 13 FoxP3 14 GFAP 15 HLA-DR 16 MPO 17 Olig2 18 P2PY12 19 Sox2 20 Sox9 21 BrM channel index names: Channel Name Channel Index CD117 1 CD11c 2 CD14 3 CD163 4 CD16 5 CD20 6 CD31 7 CD3 8 CD4 9 CD68 10 CD8a 11 CD94 12 DNA1 13 FoxP3 14 GFAP 15 HLA-DR 16 MPO 17 MeLanA 18 P2PY12 19 PMEL 20 PanCK 21

Brain metastases (BM) are associated with significant morbidity and mortality in patients with advanced cancer. Despite significant advances in surgical, radiation, and systemic therapy in recent years, the median overall survival of patients with BM is less than 1 year. The acquisition of medical images, such as computed tomography (CT) and magnetic resonance imaging (MRI), is critical for the diagnosis and stratification of patients to appropriate treatments. Radiomic analyses have the potential to improve the standard of care for patients with BM by applying artificial intelligence (AI) with already acquired medical images to predict clinical outcomes and direct the personalized care of BM patients. Herein, we outline the existing literature applying radiomics for the clinical management of BM. This includes predicting patient response to radiotherapy and identifying radiation necrosis, performing virtual biopsies to predict tumor mutation status, and determining the cancer of origin in brain tumors identified via imaging. With further development, radiomics has the potential to aid in BM patient stratification while circumventing the need for invasive tissue sampling, particularly for patients not eligible for surgical resection.

PURPOSE Non-V600 mutations comprise approximately 35% of all BRAF mutations in cancer. Many of these mutations have been identified as oncogenic drivers and can be classified into three classes according to molecular characteristics. Consensus treatment strategies for class 2 and 3 BRAF mutations have not yet been established. METHODS We performed a systematic review and meta-analysis with published reports of individual patients with cancer harboring class 2 or 3 BRAF mutations from 2010 to 2021, to assess treatment outcomes with US Food and Drug Administration–approved mitogen-activated protein kinase (MAPK) pathway targeted therapy (MAPK TT) according to BRAF class, cancer type, and MAPK TT type. Coprimary outcomes were response rate and progression-free survival. RESULTS A total of 18,167 studies were screened, identifying 80 studies with 238 patients who met inclusion criteria. This included 167 patients with class 2 and 71 patients with class 3 BRAF mutations. Overall, 77 patients achieved a treatment response. In both univariate and multivariable analyses, response rate and progression-free survival were higher among patients with class 2 compared with class 3 mutations, findings that remain when analyses are restricted to patients with melanoma or lung primary cancers. MEK ± BRAF inhibitors demonstrated greater clinical activity in class 2 compared with class 3 BRAF-mutant tumors than BRAF or EGFR inhibitors. CONCLUSION This meta-analysis suggests that MAPK TTs have clinical activity in some class 2 and 3 BRAF-mutant cancers. BRAF class may dictate responsiveness to current and emerging treatment strategies, particularly in melanoma and lung cancers. Together, this analysis provides clinical validation of predictions made on the basis of a mutation classification system established in the preclinical literature. Further evaluation with prospective clinical trials is needed for this population.

Bioenergetic perturbations driving neoplastic growth increase the production of reactive oxygen species (ROS), requiring a compensatory increase in ROS scavengers to limit oxidative stress. Intervention strategies that simultaneously induce energetic and oxidative stress therefore have therapeutic potential. Phenformin is a mitochondrial complex I inhibitor that induces bioenergetic stress. We now demonstrate that inflammatory mediators, including IFNγ and polyIC, potentiate the cytotoxicity of phenformin by inducing a parallel increase in oxidative stress through STAT1-dependent mechanisms. Indeed, STAT1 signaling downregulates NQO1, a key ROS scavenger, in many breast cancer models. Moreover, genetic ablation or pharmacological inhibition of NQO1 using β-lapachone (an NQO1 bioactivatable drug) increases oxidative stress to selectively sensitize breast cancer models, including patient derived xenografts of HER2+ and triple negative disease, to the tumoricidal effects of phenformin. We provide evidence that therapies targeting ROS scavengers increase the anti-neoplastic efficacy of mitochondrial complex I inhibitors in breast cancer., Complex I inhibition induces oxidative stress leading to cancer cell cytotoxicity. Here, the authors show, in breast cancer models, that inflammatory mediators can potentiate complex I inhibitor phenformin cytotoxicity through STAT1-mediated downregulation of the reactive oxygen species scavenger NQO1.

Background Sixty percent of surgically resected brain metastases (BrM) recur within 1 year. These recurrences have long been thought to result from the dispersion of cancer cells during surgery. We tested the alternative hypothesis that invasion of cancer cells into the adjacent brain plays a significant role in local recurrence and shortened overall survival. Methods We determined the invasion pattern of 164 surgically resected BrM and correlated with local recurrence and overall survival. We performed single-cell RNA sequencing (scRNAseq) of >15,000 cells from BrM and adjacent brain tissue. Validation of targets was performed with a novel cohort of BrM patient-derived xenografts (PDX) and patient tissues. Results We demonstrate that invasion of metastatic cancer cells into the adjacent brain is associated with local recurrence and shortened overall survival. scRNAseq of paired tumor and adjacent brain samples confirmed the existence of invasive cancer cells in the tumor-adjacent brain. Analysis of these cells identified cold-inducible RNA-binding protein (CIRBP) overexpression in invasive cancer cells compared to cancer cells located within the metastases. Applying PDX models that recapitulate the invasion pattern observed in patients, we show that CIRBP is overexpressed in highly invasive BrM and is required for efficient invasive growth in the brain. Conclusions These data demonstrate peritumoral invasion as a driver of treatment failure in BrM that is functionally mediated by CIRBP. These findings improve our understanding of the biology underlying postoperative treatment failure and lay the groundwork for rational clinical trial development based upon invasion pattern in surgically resected BrM.

INTRODUCTION LM is a debilitating condition associated with metastatic cancers, including BC. When oncogenic drivers are identified, TT represents an appealing therapeutic strategy. However, the efficacy of TT for LM is unknown as LM patients are routinely omitted from clinical trials. METHODS We conducted a systematic review and meta-analysis of individual patient data to evaluate the effectiveness of HER2-TT in HER2+ BCLM in accordance with PRISMA guidelines. TTs evaluated included trastuzumab (intrathecal (IT) or intravenous (IV)), trastuzumab-emtansine, trastuzumab-deruxtecan, and lapatinib. Primary outcome was overall survival (OS). RESULTS Of 7780 abstracts screened, 91 publications and a total of 109 patients were included in the final analysis. Patients receiving chemotherapy (either IT, IV, or as part of an antibody-drug conjugate) concurrently with HER2-TT (N=57) exhibited a median OS (mOS) of 44.0 months, compared to patients treated with targeted anti-HER2 therapies alone (N=52), which exhibited a mOS of 14.5 months (P=0.009, hazard ratio (HR): 0.538, 95% confidence interval (CI): 0.328-0.883). Patients receiving IT trastuzumab (N=83) exhibited a median progression-free survival (mPFS) and mOS of 6.0 and 21.0 months, respectively, while patients receiving IV trastuzumab (N=14) exhibited a mPFS and mOS of 6.5 and 27.0 months, respectively (PFS: P=0.31, HR: 0.712, 95% CI: 0.331-1.531; OS: P=0.68, HR: 1.154, 95% CI: 0.587-2.266). In the subgroup of patients receiving IT trastuzumab (N=58), those who concurrently received IT chemotherapy (N=48) exhibited mPFS and mOS of 5.7 and 14.0 months, respectively, while patients concurrently receiving IV chemotherapy (N=10) exhibited a mPFS and mOS of 6.0 and 27.0 months, respectively (PFS: P=0.45, HR: 1.360, 95% CI: 0.602-3.073; OS P=0.29, HR: 1.821, 95% CI: 0.630-5.260). CONCLUSIONS HER2-TT is an effective therapeutic strategy for BCLM. Patients with BCLM receiving concurrent cytotoxic chemotherapy alongside HER2-TT experience prolonged mOS. IV and IT trastuzumab are similarly effective. Univariate and multivariate analyses will be presented.

Melanoma is an immunogenic cancer with a high response rate to immune checkpoint inhibitors (ICIs). It harbors a high mutation burden compared with other cancers and, as a result, has abundant tumor-infiltrating lymphocytes (TILs) within its microenvironment. However, understanding the complex interplay between the stroma, tumor cells, and distinct TIL subsets remains a substantial challenge in immune oncology. To properly study this interplay, quantifying spatial relationships of multiple cell types within the tumor microenvironment is crucial. To address this, we used cytometry time-of-flight (CyTOF) imaging mass cytometry (IMC) to simultaneously quantify the expression of 35 protein markers, characterizing the microenvironment of 5 benign nevi and 67 melanomas. We profiled more than 220,000 individual cells to identify melanoma, lymphocyte subsets, macrophage/monocyte, and stromal cell populations, allowing for in-depth spatial quantification of the melanoma microenvironment. We found that within pretreatment melanomas, the abundance of proliferating antigen-experienced cytotoxic T cells (CD8 + CD45RO + Ki67 + ) and the proximity of antigen-experienced cytotoxic T cells to melanoma cells were associated with positive response to ICIs. Our study highlights the potential of multiplexed single-cell technology to quantify spatial cell-cell interactions within the tumor microenvironment to understand immune therapy responses.

PurposeNon-V600 mutations comprise approximately 35% of all BRAF mutations in cancer. Many of these mutations have been identified as oncogenic drivers in a wide array of cancer types and can be classified into three Classes according to molecular characteristics. Consensus treatment strategies for Class 2 and 3 BRAF mutations have not yet been established.MethodsWe performed a systematic review and meta-analysis of individual patient data to assess treatment outcomes with FDA-approved mitogen activated protein kinase pathway (MAPK) targeted therapy according to BRAF Class, cancer type and MAPK targeted therapy type. A search was conducted on literature from 2010-2021. Individual patient data was collected and analyzed from published reports of patients with cancer harboring Class 2 or 3 BRAF mutations and who received MAPK targeted therapy with available treatment response data. Co-primary outcomes were response rate (RR) and progression-free survival (PFS).Results18167 studies were screened, identifying 80 studies with 238 patients that met inclusion criteria. This included 167 patients with Class 2 and 71 patients with Class 3 BRAF mutations. Overall, 77 patients achieved a treatment response. In both univariate and multivariable analyses, RR and PFS were higher among patients with Class 2 compared to Class 3 mutations, findings that remain when analyses are restricted to patients with melanoma or lung primary cancers. MEK +/- BRAF inhibitors demonstrated greater clinical activity in Class 2 compared to Class 3 BRAF mutant tumors than BRAF or EGFR inhibitors.ConclusionsThis meta-analysis suggests that MAPK targeted therapies have clinical activity in some Class 2 and 3 BRAF mutant cancers. BRAF Class may dictate responsiveness to current and emerging treatment strategies, particularly in metastatic melanoma and lung cancers. Together, this analysis provides clinical validation of predictions made based on a mutation classification system established in the preclinical literature. Further evaluation with prospective clinical trials is needed for this population.

Given recent advances in the treatment of cancer, patients are surviving longer but frequently develop treatment‐resistant and inoperable metastases. Biomedical research has advanced to the stage where in‐depth study of these lesions is feasible, with the goal of further refining our understanding of metastatic dissemination, therapeutic resistance and inoperable tumors. However, there is a lack of tissue specimens derived from multiple metastatic sites within the same patient that would permit the study of these processes. Furthermore, patients with rapidly progressing or metastatic disease are rarely candidates for surgery, making those most in need of innovation and discovery extremely difficult to study. For this reason, post‐mortem tissue donation programs are an approach that is quickly gaining traction in the cancer research community. Herein, we discuss what post‐mortem tissue donation entails, attitudes towards these procedures, and highlight important studies already utilizing these resources. In addition, we propose future directions for use of this tissue that can directly improve clinical management of advanced cancer patients.

It is important to strengthen critical thinking and scientific writing abilities during medical training to support trainees in their research endeavors and prepare students for careers in academic medicine. This commentary describes an interactive workshop to encourage student engagement with scientific literature and contribution to scholarly discourse by writing letters to the editor (LTEs). Students in the MD-PhD program at McGill University were asked to identify an article from a high-impact journal and think about ways in which they could address its scientific content. Students completed this preparation on their own time and then attended a 90-minute workshop where their LTEs were finalized and submitted. The LTE workshops were conducted in 2017 and 2019, and student participation and informal feedback indicated that perceptions of the workshops were positive. The workshops provided students an opportunity to strengthen their critical appraisal and academic communication skills while also contributing to the scientific literature. Letters written by aspiring and practicing physicians add valuable clinical insight to the literature and promote physician engagement with research. Strategies to support the adoption of LTE workshops include incorporating them into longitudinal curricula in medical school and integrating them into journal clubs during residency or fellowship.

Although combination BRAF/MEK inhibition has produced significant survival benefits for BRAF p.V600 mutant melanomas, targeted therapies approved for BRAF non-p.V600 mutant melanomas remain limited. Through the analysis of 772 cutaneous melanoma exomes, we reveal that BRAF non-p.V600 mutations co-occurs more frequently with NF1 loss, but not with oncogenic NRAS mutations, than expected by chance. We present cell signaling data, which demonstrate that BRAF non-p.V600 mutants can signal as monomers and dimers within an NF1 loss context. Concordantly, BRAF inhibitors that inhibit both monomeric and dimeric BRAF synergize with MEK inhibition to significantly reduce cell viability in vitro and tumor growth in vivo in BRAF non-p.V600 mutant melanomas with co-occurring NF1 loss-of-function mutations. Our data suggest that patients harboring BRAF non-p.V600 mutant melanomas may benefit from current FDA-approved BRAF/MEK inhibitor combination therapy currently reserved for BRAF p.V600 mutant patients.

In the early developmental phase of a postmortem rapid tissue donation (rtd) program for patients with metastatic cancer, we surveyed health care professionals (hcps) and oncology patients at the McGill University Health Centre (muhc) to assess their knowledge and attitudes pertaining to rtd from metastatic cancer patients for research purposes. A 23-item survey was developed and distributed to hcps at tumour board meetings, and a related 26-item survey was developed and distributed to oncology patients at the muhc Cedars Cancer Centre. The survey attracted participation from 73 hcps, including 37 attending physicians, and 102 oncology patients. Despite the fact that 88% of hcps rated their knowledge of rtd as none or limited, 42% indicated that they would feel comfortable discussing rtd with their cancer patients. Of the responding hcps, 67% indicated that their current knowledge of rtd would affect their decision to discuss such a program with patients, which implies the importance of education for hcps to facilitate enrolment of patients into a rtd program. Of responding patients, 78% indicated that they would not be uncomfortable if their doctor discussed rtd with them, and 61% indicated that they would like it if their doctor were to discuss rtd with them. The hcps and patients felt that the best time for patients to be approached about consenting to a rtd program would be at the transition to palliative care when no treatment options remain. At the muhc, hcps and patients are generally enthusiastic about adopting a rtd program for patients with metastatic cancer. Education of hcps and patients will be an important determinant of the program&rsquo, s success.

Background: Cold-Inducible RNA Binding Protein (CIRBP) has been implicated in cancer initiation. Moreover, we have previously identified an association of CIRBP with the invasive growth of parenchymal brain metastases. Using a patient-derived xenograft (PDX) model, in which cells implanted in the mouse mammary fat pad spontaneously metastasize to the leptomeninges, we identified CIRBP as being elevated in leptomeningeal metastases (LM) compared to matched primary mammary tumors. LM grow in the subarachnoid space that harbors the cerebral spinal fluid (CSF). The leptomeninges represent an inhospitable environment for disseminated cancer cells since the CSF is mitogen and nutrient poor. To investigate the importance of CIRBP for metastatic breast cancer cells in the leptomeninges, we stably reduced CIRBP expression in MDA-MB-231 cells and performed mammary fat pad and cranial injections. CIRBP knockdown had no influence on primary tumor growth, but diminished growth within the brain. Hypothesis: We hypothesize that CIRBP functions as a stress response protein enabling cancer cells to grow in the harsh environment of the CSF. Results: In response to various cellular stressors, such as hypothermia, hypoxia or UV irradiation, CIRBP can translocate from the nucleus to the cytoplasm. We show that culturing MDA-MB-231 cells in artificial CSF (aCSF) also causes CIRBP relocation from nucleus to cytoplasm. Using RNA-IP approaches, we have identified mRNAs bound by CIRBP in breast cancer cells treated with aCSF. Ultimately, we will determine whether any of the identified CIRBP-regulated targets contribute to the formation of LM. Finally, we have generated CIRBP variants that are confined either to the nucleus or the cytoplasm. We are currently assessing the ability of these compartment-restricted CIRBP proteins to promote the formation of central nervous system metastases. Conclusions: We have identified CIRBP as a promoter of leptomeningeal metastasis. Our results have begun to reveal the mechanisms through which CIRBP mediates this process. Citation Format: Rima Ezzeddine, Matthew Dankner, Paul Savage, Steven Hebert, William Brothers, Matthew G. Annis, Sarah M. Maritan, Marc R. Fabian, Claudia Kleinman, Morag Park, Peter M. Siegel. CIRBP is a functional mediator of leptomeningeal metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2436.

Background: Brain metastases (BrM) with highly invasive (HI) growth patterns are associated with shortened local recurrence free- and overall survival compared to minimally invasive (MI) lesions (Dankner et al. 2021). Compared to MI lesions, HI BrM form abundant contacts with cells in the peritumoral brain, particularly GFAP+ reactive astrocytes (RAs). RAs expressing phosphorylated STAT3 (pSTAT3+ GFAP+ cells) have been shown to be required for BrM colonization and outgrowth (Priego et al. 2018). Here, we investigate the role of pSTAT3+ cells in the brain microenvironment in promoting invasive growth. Methods: We performed immunohistochemistry to identify pSTAT3+ GFAP+ cells in HI and MI human and patient-derived xenograft BrM. We assessed how pharmacological inhibition or genetic ablation of STAT3 affected HI and MI BrM growth in vivo with patient-derived xenograft and syngeneic models of BrM. The secretome of STAT3+ RAs was interrogated to identify STAT3 target genes that could drive invasive cancer growth. scRNA-Seq from patients with highly invasive brain metastases was used to examine the expression of candidate invasion factors in distinct cell types within the brain. Finally, cancer cell invasion was modeled in vitro using a brain slice-tumor co-culture assay. Results: HI BrM displayed increased pSTAT3+GFAP+ cells compared to MI lesions. Pharmacological STAT3i with Legasil (Silibinin) or genetic ablation of STAT3 specifically in RAs decreased in vivo growth of HI, but not MI, BrM. Brain slice cultures treated with STAT3-activating cytokines induced cancer cell invasion, a response that was ablated with STAT3i. Chi3L1 was identified as a STAT3 target gene expressed abundantly by stromal cells in the BrM microenvironment. Cancer cells treated with recombinant Chi3L1 showed enhanced invasion into brain slice cultures compared to control-treated cells. Conclusions: pSTAT3+GFAP+ cells are over-represented in HI BrM, rendering HI BrM preferentially sensitive to STAT3i. pSTAT3+ stromal cells functionally contribute to BrM invasion within the brain, in part through Chi3L1. This work nominates HI histopathological growth pattern as a predictive biomarker of response to STAT3i, and highlights Chi3L1 as a novel therapeutic target for the management of HI BrM. Citation Format: Matthew Dankner, Sarah M. Maritan, Neibla Priego, Javad Nadaf, Andy Nkili, Rebecca Zhuang, Georgia Kruck, Dongmei Zuo, Alexander Nowakowski, Yanis Inglebert, Paul Savage, Morag Park, Marie-Christine Guiot, Anne McKinney, William J. Muller, Manuel Valiente, Kevin Petrecca, Peter M. Siegel. pSTAT3+ stromal cells drive the invasive growth of brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1569.

Purpose: Dual MAPK pathway inhibition (dMAPKi) with BRAF and MEK inhibitors improves survival in BRAF V600E/K mutant melanoma, but the efficacy of dMAPKi in non-V600 BRAF mutant tumors is poorly understood. We sought to characterize the responsiveness of class II (enhanced kinase activity, dimerization dependent) BRAF mutant melanoma to dMAPKi. Experimental Design: Tumors from patients with BRAF wild-type (WT), V600E (class I), and L597S (class II) metastatic melanoma were used to generate patient-derived xenografts (PDX). We assembled a panel of melanoma cell lines with class IIa (activation segment) or IIb (p-loop) mutations and compared these with WT or V600E/K BRAF mutant cells. Cell lines and PDXs were treated with BRAFi (vemurafenib, dabrafenib, encorafenib, and LY3009120), MEKi (cobimetinib, trametinib, and binimetinib), or the combination. We identified 2 patients with BRAF L597S metastatic melanoma who were treated with dMAPKi. Results: BRAFi impaired MAPK signaling and cell growth in class I and II BRAF mutant cells. dMAPKi was more effective than either single MAPKi at inhibiting cell growth in all class II BRAF mutant cells tested. dMAPKi caused tumor regression in two melanoma PDXs with class II BRAF mutations and prolonged survival of mice with class II BRAF mutant melanoma brain metastases. Two patients with BRAF L597S mutant melanoma clinically responded to dMAPKi. Conclusions: Class II BRAF mutant melanoma is growth inhibited by dMAPKi. Responses to dMAPKi have been observed in 2 patients with class II BRAF mutant melanoma. These data provide rationale for clinical investigation of dMAPKi in patients with class II BRAF mutant metastatic melanoma. See related commentary by Johnson and Dahlman, p. 6107.

BRAF mutations are found in up to 10% of colorectal cancers (CRC). Whereas the majority of BRAF mutant CRCs harbor V600 mutations, up to 25% express non-V600 BRAF mutations. It has been established that BRAF V600E mutations in CRC predict unresponsiveness to epidermal growth factor receptor (EGFR) inhibition—cetuximab and/or panitumumab—as a result of the constitutive activation of the mitogen-activated protein kinase pathway downstream of EGFR signaling. As more centers begin using next-generation sequencing assays to detect BRAF mutations, oncologists are more frequently confronted with treating patients with non-V600 BRAF mutations. In many instances, clinicians may be hesitant to use EGFR inhibitors for these patients, as it is largely assumed that tumors with non-V600 BRAF mutations activate the mitogen-activated protein kinase pathway in a similar manner to RAS or BRAF V600E mutations and would therefore be equally refractory to EGFR inhibition; however, the evidence that currently exists to substantiate this claim is mixed and incomplete. Recent data demonstrate that non-V600 BRAF mutant CRC is a distinct clinical entity with a favorable prognosis compared with CRC with V600E mutations. Preclinical data and several case reports suggest that a subset of BRAF non-V600 mutations that impair the protein's kinase activity may in fact confer heightened sensitivity to EGFR inhibition because of dependency on upstream receptor tyrosine kinase signaling. This review summarizes the clinical characteristics and targeted therapy approaches for non-V600 BRAF mutant CRCs, speculates on the value of non-V600 BRAF mutations as predictive biomarkers of responsiveness to EGFR inhibitors, and highlights outstanding questions in this emerging area of precision oncology.

Simple Summary Leptomeningeal metastases occur when cancer cells reach the fluid-filled space that surrounds the brain and spinal cord. This type of brain lesion is most prevalent in patients with lung cancer, breast cancer and melanoma. While the clinical characteristics of leptomeningeal metastases have been well described, fundamental research revealing insights into how these lesions develop and grow has only just begun. This review describes the clinical and basic science literature surrounding leptomeningeal metastases from adult solid tumors, proposing novel ways the clinical and research communities can work together to make important advances for patients suffering from this devastating complication of advanced cancer. Abstract Metastasis to the central nervous system occurs in approximately 20% of patients with advanced solid cancers such as lung cancer, breast cancer, and melanoma. While central nervous system metastases most commonly form in the brain parenchyma, metastatic cancer cells may also reside in the subarachnoid space surrounding the brain and spinal cord to form tumors called leptomeningeal metastases. Leptomeningeal metastasis involves cancer cells that reach the subarachnoid space and proliferate in the cerebrospinal fluid compartment within the leptomeninges, a sequela associated with a myriad of symptoms and poor prognosis. Cancer cells exposed to cerebrospinal fluid in the leptomeninges must contend with a unique microenvironment from those that establish within the brain or other organs. Leptomeningeal lesions provide a formidable clinical challenge due to their often-diffuse infiltration within the subarachnoid space. The molecular mechanisms that promote the establishment of leptomeningeal metastases have begun to be elucidated, demonstrating that it is a biological entity distinct from parenchymal brain metastases and is associated with specific molecular drivers. In this review, we outline the current state of knowledge pertaining to the diagnosis, treatment, and molecular underpinnings of leptomeningeal metastasis.

BACKGROUND Surgery as a single modality for the treatment of brain metastases (BrM) results in local recurrence (LR) in 60% of patients. These failure rates are reduced by half with post-operative radiotherapy. The non-invasive nature of BrM has led to the assumption that local recurrence is caused by spillage of cancer cells into the surgical cavity at the time of surgery. We present evidence suggesting that invasion of metastatic cancer cells into the adjacent brain is present in the majority of BrM and is associated with LR, leptomeningeal metastasis (LM), and overall survival (OS). METHODS We assessed the histopathological growth pattern (HGP) of 164 surgically resected BrM. HGP was correlated with LR, LM and OS. Single-cell transcriptomics (scRNAseq) was performed on 15,615 cells from metastasis center (MC) and surrounding brain (SB) adjacent to the tumor. N=30 orthotopic patient-derived xenograft models (OPDX) were established from BrM. RESULTS 56/164 (34%) BrM specimens showed a minimally invasive (MI) HGP between the tumor and adjacent brain while 108/164 (66%) showed significant invasion of tumor lobules or single-cells into the brain (HI-HGP). HI-HGP was associated with LR, LM and shortened OS in BrM patients. scRNAseq identified abundant cancer cells in SB that overexpressed pathways and genes involved in cell survival and stress adaptation compared to matched cancer cells in MC. Validation of these targets with immunohistochemistry in patient and OPDX tissues revealed cold-inducible RNA binding protein (CIRBP) overexpression in HI-HGP patient and OPDX BrM. Modulation of CIRBP expression in OPDX and cell line models of HI-HGP BrM delayed BrM progression and extended OS. CONCLUSION HI-HGP is a poor prognostic indicator in patients with surgically resected BrM, establishing HGP as an important prognostic factor that should be considered by clinicians treating BrM patients. We identify CIRBP as a functional mediator of this process.

The Canadian government recently announced, to much fanfare, that they have begun procuring the supplies that will be essential for mass vaccination against COVID-19, beginning with an agreement for 75 million syringes, alcohol swabs and bandages. This is certainly good news, and it is absolutely worthwhile to think about these possibly overlooked factors needed to effectively vaccinate the population. But what will we vaccinate them with? Dankner and Michell-Robinson argue that in the current political climate, the Canadian Government must act now to invest in securing early vaccine doses from promising trials as well as make long term plans to bolster the Canadian industrial scientific sector in order to avoid future issues with drug development during international crises.

Subsets of breast tumors present major clinical challenges, including triple-negative, metastatic/recurrent disease and rare histologies. Here, we developed 37 patient-derived xenografts (PDX) from these difficult-to-treat cancers to interrogate their molecular composition and functional biology. Whole-genome and transcriptome sequencing and reverse-phase protein arrays revealed that PDXs conserve the molecular landscape of their corresponding patient tumors. Metastatic potential varied between PDXs, where low-penetrance lung micrometastases were most common, though a subset of models displayed high rates of dissemination in organotropic or diffuse patterns consistent with what was observed clinically. Chemosensitivity profiling was performed in vivo with standard-of-care agents, where multi-drug chemoresistance was retained upon xenotransplantation. Consolidating chemogenomic data identified actionable features in the majority of PDXs, and marked regressions were observed in a subset that was evaluated in vivo. Together, this clinically-annotated PDX library with comprehensive molecular and phenotypic profiling serves as a resource for preclinical studies on difficult-to-treat breast tumors., Savage et al. employ whole-genome, transcriptome sequencing and reverse-phase protein arrays on 37 developed breast cancer patient-derived xenografts (PDX) models to identify potential therapeutic targets, metastatic potential and chemosensitivity. This PDX library with comprehensive molecular and phenotypic profiling could serve as a resource for preclinical studies on difficult-to-treat breast tumors.

Background The p66ShcA redox protein is the longest isoform of the Shc1 gene and is variably expressed in breast cancers. In response to a variety of stress stimuli, p66ShcA becomes phosphorylated on serine 36, which allows it to translocate from the cytoplasm to the mitochondria where it stimulates the formation of reactive oxygen species (ROS). Conflicting studies suggest both pro- and anti-tumorigenic functions for p66ShcA, which prompted us to examine the contribution of tumor cell-intrinsic functions of p66ShcA during breast cancer metastasis. Methods We tested whether p66ShcA impacts the lung-metastatic ability of breast cancer cells. Breast cancer cells characteristic of the ErbB2+/luminal (NIC) or basal (4T1) subtypes were engineered to overexpress p66ShcA. In addition, lung-metastatic 4T1 variants (4T1-537) were engineered to lack endogenous p66ShcA via Crispr/Cas9 genomic editing. p66ShcA null cells were then reconstituted with wild-type p66ShcA or a mutant (S36A) that cannot translocate to the mitochondria, thereby lacking the ability to stimulate mitochondrial-dependent ROS production. These cells were tested for their ability to form spontaneous metastases from the primary site or seed and colonize the lung in experimental (tail vein) metastasis assays. These cells were further characterized with respect to their migration rates, focal adhesion dynamics, and resistance to anoikis in vitro. Finally, their ability to survive in circulation and seed the lungs of mice was assessed in vivo. Results We show that p66ShcA increases the lung-metastatic potential of breast cancer cells by augmenting their ability to navigate each stage of the metastatic cascade. A non-phosphorylatable p66ShcA-S36A mutant, which cannot translocate to the mitochondria, still potentiated breast cancer cell migration, lung colonization, and growth of secondary lung metastases. However, breast cancer cell survival in the circulation uniquely required an intact p66ShcA S36 phosphorylation site. Conclusion This study provides the first evidence that both mitochondrial and non-mitochondrial p66ShcA pools collaborate in breast cancer cells to promote their maximal metastatic fitness.

Triple-negative breast cancer (TNBC) is typically aggressive, difficult to treat, and commonly metastasizes to the visceral organs and soft tissues, including the lungs and the brain. Taxanes represent the most effective and widely used therapeutic class in metastatic TNBC but possess limiting adverse effects that often result in a delay, reduction, or cessation of their use. DZ-2384 is a candidate microtubule-targeting agent with a distinct mechanism of action and strong activity in several preclinical cancer models, with reduced toxicities. DZ-2384 is highly effective in patient-derived taxane-sensitive and taxane-resistant xenograft models of TNBC at lower doses and over a wider range relative to paclitaxel. When comparing compound exposure at minimum effective doses relative to safe exposure levels, the therapeutic window for DZ-2384 is 14-32 compared with 2.0 and less than 2.8 for paclitaxel and docetaxel, respectively. DZ-2384 is effective at reducing brain metastatic lesions when used at maximum tolerated doses and is equivalent to paclitaxel. Drug distribution experiments indicate that DZ-2384 is taken up more efficiently by tumor tissue but at equivalent levels in the brain compared with paclitaxel. Selective DZ-2384 uptake by tumor tissue may in part account for its wider therapeutic window compared with taxanes. In view of the current clinical efforts to combine chemotherapy with immune checkpoint inhibitors, we demonstrate that DZ-2384 acts synergistically with anti-CTLA-4 immunotherapy in a syngeneic murine model. These results demonstrate that DZ-2384 has a superior pharmacologic profile over currently used taxanes and is a promising therapeutic agent for the treatment of metastatic TNBC.

The RAS-RAF-MEK-ERK signaling cascade is among the most frequently mutated pathways in human cancer. Approximately 50% of melanoma patients possess a druggable hotspot V600E/K mutation in the BRAF protein kinase. FDA-approved combination therapies of BRAF and MEK inhibitors are available that provide survival benefits to patients with a BRAF V600 mutation. Non-V600 BRAF mutants are found in many cancers, and are more prevalent than V600 mutations in certain tumor types. For example, between 50-80% of BRAF mutations in non-small cell lung cancer and 22-30% in colorectal cancer encode for non-V600 mutants. As next generation sequencing becomes increasingly used in clinical practice, oncologists are frequently identifying non-V600 BRAF mutations in their patient's tumors, but are uncertain of viable therapeutic options that could be employed for optimal treatment. From recent studies, a new classification system is emerging for BRAF mutations based on biochemical and signaling mechanisms associated with these mutants. Class I BRAF mutations affect amino acid V600 and signal as RAS-independent active monomers, class II mutations function as RAS-independent activated dimers, and class III mutations are kinase impaired but increase signaling through the MAPK pathway due to enhanced RAS binding and subsequent CRAF activation. These distinct classes of BRAF mutations predict response to targeted therapies and have important implications for future drug development. Herein, we discuss pre-clinical and clinical findings that may lead to improved treatments for all classes of BRAF mutant cancers.

Background Brain metastases (BrM) with a highly invasive (HI) histological growth pattern are associated with poor prognosis compared to minimally invasive (MI) masses. Compared to MI lesions, HI BrM form greater contacts with cells in the peritumoral brain, particularly reactive astrocytes (RAs). RAs expressing phosphorylated STAT3 (pSTAT3+RAs) have been shown to promote BrM colonization. Here, we investigate the role of pSTAT3+RAs in promoting invasive growth of HI BrM. Methods We performed immunohistochemistry to identify pSTAT3+RAs in HI and MI human and patient-derived xenograft BrM. We assessed how pharmacological STAT3 inhibition or RA-specific STAT3 genetic ablation affected HI and MI BrM growth in vivo. scRNA-seq data generated from HI BrM astrocytes were integrated with published RA secretome data to identify STAT3 targets expressed by RAs that may drive invasion. Cancer cell invasion was modeled in vitro using a brain slice-tumor co-culture assay. Results HI BrM display increased pSTAT3-positivity within RAs when compared to MI lesions. Pharmacological STAT3 inhibition with Legasil (Silibinin) or genetic ablation decreased in vivo growth of HI, but not MI, BrM. Brain slice cultures treated with STAT3-activating cytokines induced cancer cell invasion, a response that was ablated following STAT3 inhibition. Chi3L1 was identified as a STAT3 target expressed by RAs. Cancer cells treated with recombinant Chi3L1 showed greater invasion into brain slice cultures compared to untreated cells. Conclusions pSTAT3+RAs are over-represented in HI BrM, rendering HI BrM preferentially sensitive to STAT3 inhibition. pSTAT3+RAs functionally contribute to BrM invasion within the brain, in part through Chi3L1-mediated activity. This work identifies STAT3 and Chi3L1 as clinically relevant therapeutic targets in management of HI BrM.

3089 Background: Oncogenic nonV600 BRAF mutations (muts) can be classified according to distinct molecular characteristics. TT strategies for class 2 and 3 BRAF muts have not been established. In recent years there have been numerous reports of clinical activity for various TT in pts with nonV600 muts. We performed a systematic scoping review and meta-analysis to assess treatment outcomes with MAPK TT according to BRAF class, cancer type and TT type. Methods: An extensive literature search was conducted from 2010-20. All studies were independently reviewed and extracted by 2 reviewers and in accordance with PRISMA guidelines. Individual patient level data were collected and analyzed from studies that met the following inclusion criteria: published reports of 1) advanced cancer pts with; 2) class 2 or class 3 nonV600 BRAF muts; 3) who received MAPK TT; 4) with treatment response (TR) data available. Primary outcome was overall TR rate (TRR). To assess differences between groups, odds ratios (OR) were calculated using a multi-level mixed-effects logistic regression model. Results: 15,171 studies were screened and 168 were included for data extraction. We identified 100 studies with a total of 396 pts that met inclusion criteria. There were 17 reports (161 pts) of prospective clinical trials and 83 retrospective studies (235 pts). RECIST criteria were used for TR assessment in 183 (46%) pts. The entire study included 280 pts with class 2 and 116 pts with class 3 BRAF muts. Overall, 111 (28%) pts achieved a TR. TRR according to primary tumor type, BRAF class, and TT type is indicated in Table. TRR was lower in reports of prospective studies compared to retrospective studies (OR 0.14, P = 0.002), and in studies that employed RECIST criteria vs. those that didn’t (OR 0.29, P = 0.044). TRR was higher among pts with class 2 muts vs. those with class 3 muts (OR 2.21, P = 0.042). Conclusions: These data establish that MAPK TT have demonstrated clinical activity in cancers with oncogenic nonV600 mutations, and that BRAF mutation class may dictate responsiveness to different TT strategies. TRR may be over-estimated in the retrospective literature. This analysis will be valuable for molecular tumor boards and to guide future clinical trial design. Prospective clinical trials of TT in this pt population are warranted.[Table: see text]

BACKGROUND Brain metastasis (BrM) patients treated with surgery and radiotherapy frequently experience local recurrence (LR), leptomeningeal metastasis (LM), and poor overall survival (OS). We sought to correlate the presence of invasive or circumscribed histopathological growth pattern, observed in the BrM lesion and surrounding brain, with these outcomes, and to study molecular mediators of parenchymal invasion. METHODS We assessed the HGP of H&E-stained slides from 164 surgically resected BrM from 147 patients. HGP was correlated with incidence of LR, LM and OS. Single-cell RNA sequencing (scRNAseq) was performed on three invasive HGP patients, sampling the metastasis center (MC) and surrounding brain (SB) outside of the contrast-enhancing region. Orthotopic patient-derived xenograft models (OPDX) were established from N=30 brain metastasis via intracranial propagation. RESULTS 56/164 BrM specimens (34%) showed a circumscribed growth pattern between the tumor and adjacent brain (cHGP) while 108/164 (66%) showed significant invasion of tumor lobules or single cells into the brain parenchyma (iHGP). iHGP was associated with LR, LM and shortened OS in BrM patients. OPDX models of BrM retain features of patient BrM, including HGP. scRNAseq identified abundant cancer cells in SB that overexpressed a number of genes involved in cell survival, invasion and metastasis compared to matched cancer cells in MC. Validation of these targets with immunohistochemistry in patient and OPDX tissues revealed cold-inducible RNA binding protein (CIRBP) overexpression in iHGP patient and OPDX BrM. Modulation of CIRBP expression in OPDX and cell line models of iHGP BrM delayed BrM progression and extended OS. CONCLUSION iHGP is a poor prognostic indicator in patients with surgically resected BrM, establishing HGP as an important prognostic factor that should be considered by clinicians treating BrM patients. We identify CIRBP as a functional mediator of this process.

Prostate cancer (PC) commonly metastasizes to the bone, resulting in pathologic fractures and poor prognosis. CCN3/nephroblastoma overexpressed is a secreted protein with a known role in promoting breast cancer metastasis to bone. However, in PC, CCN3 has been ascribed conflicting roles; some studies suggest that CCN3 promotes PC metastasis, whereas others argue a tumor suppressor role for CCN3 in this disease. Indeed, in the latter context, CCN3 has been shown to sequester the androgen receptor (AR) and suppress AR signaling. In the present study, we demonstrate that CCN3 functions as a bone-metastatic mediator, which is dependent on its C-terminal domain for this function. Analysis of tissue microarrays comprising >1500 primary PC patient radical prostatectomy specimens reveals that CCN3 expression correlates with aggressive disease and is negatively correlated with the expression of prostate-specific antigen, a marker of AR signaling. Together, these findings point to CCN3 as a biomarker to predict PC aggressiveness while providing clarity on its role as a functional mediator of PC bone metastasis.

CEACAM1 is an extensively studied cell surface molecule with established functions in multiple cancer types, as well as in various compartments of the immune system. Due to its multi-faceted role as a recently appreciated immune checkpoint inhibitor and tumor marker, CEACAM1 is an attractive target for cancer immunotherapy. Herein, we highlight CEACAM1's function in various immune compartments and cancer types, including in the context of metastatic disease. This review outlines CEACAM1's role as a therapeutic target for cancer treatment in light of these properties.

Background: Prostate cancer commonly metastasizes to the bone, resulting in pathological fractures and poor prognosis. CCN3/NOV (Nephroblastoma overexpressed) is a secreted protein with a known role in breast cancer metastasis to bone. However, in prostate cancer, CCN3 has been ascribed conflicting roles; some studies suggest that CCN3 promotes prostate cancer metastasis while others argue a tumor suppressor role for CCN3 in this disease. Indeed, in the latter context, CCN3 has been shown to sequester the androgen receptor (AR) and suppress AR signaling. The C-terminal domain of CCN3 is thought to mediate many the protein’s pro-metastatic functions given its role in binding to growth factors and promoting dimerization of CCN family members. We hypothesize that the CCN3 CT domain is required to promote osteolytic PC bone metastasis and that CCN3 represents a prognostic biomarker in primary PC tumors to predict recurrence to bone. Methods: CCN3WT and CCN3ΔCT were overexpressed in LNCaP C4-2 cells. The role of CCN3 was assessed with in vitro proliferation, migration and invasion assays, and in vivo through intracardiac injection in male Nude mice (Nu/Nu). Ex vivo µCT scans were performed on murine bone metastasis specimens. CCN3 expression was assessed in two unique tissue microarrays (TMA) comprising over 1500 human primary prostate tumor using different anti-CCN3 antibodies with immunohistochemistry and immunohistofluorescnece, respectively. Results: While CCN3WT and CCN3ΔCT had little effect in vitro on cell proliferation, migration or invasion, intracardiac injection of CCN3WT resulted in increased incidence of bone metastasis compared to empty vector control and CCN3ΔCT. Ex vivo µCT revealed decreased bone mineral density in bones from mice injected with CCN3WT cells compared to empty vector control and CCN3ΔCT expressing LNCaP C4-2 cells. In both TMAs studied, high CCN3 expression in tumor epithelium correlated with increased risk of biochemical relapse and bone metastasis at 5 years and 15 years post- surgical resection, respectively. Conclusion: CCN3 requires its C-terminal domain for its bone metastatic function, and CCN3 is correlated with aggressive disease biology in primary prostate cancer specimens. These findings point to CCN3 protein expression as a biomarker that can be useful in predicting prostate cancer aggressiveness and recurrence to bone, while providing clarity on CCN3’s functional role as a mediator of prostate cancer bone metastasis. Citation Format: Matthew Dankner, Veronique Ouellet, Laudine Desreumaux-Communal, Estelle Schmitt, Dru Perkins, Matthew G. Annis, Veronique Barres, Christine Caron, Anne-Marie Mes-Masson, Fred Saad, Peter M. Siegel. CCN3 is a prognostic biomarker and functional mediator of prostate cancer bone metastasis [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 3134.

e23005 Background: In the early developmental phase of a post-mortem Rapid Tissue Donation (RTD) program for metastatic cancer patients, we surveyed health care professionals (HCPs) and oncology patients at the McGill University Health Centre (MUHC) to assess their knowledge and attitudes pertaining to RTD from metastatic cancer patients for research purposes. Methods: A 23-item survey was developed and distributed to HCPs at tumour board meetings, and a related 26-item survey was developed and distributed to oncology patients at the MUHC Cedars Cancer Centre. Results: 73 HCPs, including 37 attending physicians, and 102 oncology patients participated in the study. Despite the fact that 88% of HCPs rated their knowledge of RTD as none or limited, 42% indicated that they would feel comfortable discussing RTD with their cancer patients. 67% of HCPs indicated that their current knowledge of RTD would impact their decision to discuss such a program with patients, implying the importance of educating HCPs to facilitate enrolment of patients into an RTD program. 78% of patients indicated that they would not be uncomfortable if their doctor discussed RTD with them, and 61% indicated that they would like for their doctor to discuss RTD with them. HCPs and patients felt that the best time for patients to be approached about consenting to an RTD program is in the transition to palliative care when there are no treatment options remaining. Conclusions: HCPs and patients at the MUHC are generally enthusiastic about adopting an RTD program for metastatic cancer patients. Education of HCPs and patients will be an important determinant of the program’s success.

We read with great interest the recent article by Dagogo-Jack and colleagues, wherein they interrogated the clinical outcomes of patients with lung cancer whose tumors expressed different classes of BRAF mutations ([1][1]). Clinicians are increasingly requesting next-generation sequencing analyses

182 Background: Prostate cancer commonly metastasizes to the bone, resulting in pathological fractures and poor prognosis. CCN3/NOV (Nephroblastoma overexpressed) has been implicated in promoting the formation of osteolytic prostate cancer (PC) bone metastases. The C-terminal domain of CCN3 binds growth factors, heparin sulfate proteoglycans, activates Notch signaling and promotes dimerization of CCN family members. We hypothesize that the CCN3 CT domain is required to promote osteolytic PC bone metastasis and that CCN3 represents a prognostic biomarker in primary PC tumors to predict recurrence to bone. Methods: CCN3WT and CCN3∆CT were overexpressed in LNCaP C4-2 cells. The role of CCN3 was assessed with in vitro proliferation, migration and invasion assays, and in vivo through intracardiac injection in male Nude mice (Nu/Nu). Ex vivo µCT scans were performed on bone specimens. CCN3 expression was assessed in two unique tissue microarrays (TMA) comprising over 1,500 primary prostate tumor using different anti-CCN3 antibodies with immunohistochemistry and immunohistofluorescnece, respectively. Results: While CCN3WT and CCN3∆CT had little effect in vitro on cell proliferation, migration or invasion, intracardiac injection of CCN3WT resulted in increased incidence of bone metastasis compared to empty vector control and CCN3∆CT. Ex vivo µCT revealed decreased bone mineral density in bones from mice injected with CCN3WT cells compared to control and CCN3∆CT expressing cells. In both TMAs studied, high CCN3 expression in tumor epithelium correlated with increased risk of biochemical relapse and bone metastasis at 5 years and 15 years post-resection, respectively. Conclusions: CCN3 requires its C-terminal domain for its bone metastatic function, and CCN3 is correlated with aggressive disease biology in prostate cancer. These findings point to CCN3 as a biomarker that can be useful to predict prostate cancer aggressiveness, while providing clarity on its role as a functional mediator of prostate cancer bone metastasis.

12093Background: dMAPKi with BRAFi and MEKi improves survival in BRAF V600E/K mt MM, but the effects of these inhibitors on nonV600 BRAF mt MM is poorly understood. We sought to characterize nonV60...