ALBERT

Description: Renal medullary carcinoma (RMC) is a rare and deadly kidney cancer in patients of African descent with sickle cell trait. We have developed faithful patient-derived RMC models and using whole-genome sequencing, we identified loss-of-function intronic fusion events in one SMARCB1 allele with concurrent loss of the other allele. Biochemical and functional characterization of these models revealed that RMC requires the loss of SMARCB1 for survival. Through integration of RNAi and CRISPR-Cas9 loss-of-function genetic screens and a small-molecule screen, we found that the ubiquitin-proteasome system (UPS) was essential in RMC. Inhibition of the UPS caused a G2/M arrest due to constitutive accumulation of cyclin B1. These observations extend across cancers that harbor SMARCB1 loss, which also require expression of the E2 ubiquitin-conjugating enzyme, UBE2C. Our studies identify a synthetic lethal relationship between SMARCB1-deficient cancers and reliance on the UPS which provides the foundation for a mechanism-informed clinical trial with proteasome inhibitors.

Description: Abstract 1586 Background Mantle cell lymphoma (MCL) is a subtype of B-cell non-Hodgkin lymphoma (NHL) characterized by the t(11;14) translocation and concomitant over-expression of cyclin D1. MCL has a variable natural history; while some patients have prolonged survival similar to other indolent B-cell lymphomas, most follow an aggressive course with short survival. While the t(11;14) is pathognomonic of MCL, it is not necessary for disease pathogenesis, as a subset of MCL cases lack the translocation. Furthermore, in vivo models demonstrate that cyclin D1 over-expression alone is unable to bring about the disease, and that deregulation of additional cellular pathways is required for its pathogenesis. Assessment of microRNA (miR) expression in MCL may help determine mechanisms of gene deregulation and reveal pathways involved in disease pathogenesis. In this study we examined MCL in relation to both aggressive and indolent B-cell NHL to determine a miR signature that characterizes MCL. Design and Methods Total RNA from a training set of 36 B-cell NHL cases (19 indolent and 17 aggressive) and 32 MCL was applied to a high-throughput quantitative real-time PCR platform assessing the expression of 365 miRs [TaqMan Human MicroRNA Array v1.0 (Early Access) or TLDA]. miRs that were differentially expressed between MCL and aggressive NHL, and between MCL and indolent NHL were then validated using RNA from a second, independent, set of B-cell NHL cases (28 indolent and 28 aggressive) and 50 MCL cases. Validated miRs were determined and potential targets for each miR were examined. A map of targets common to the MCL miR signature was created, revealing important proteins involved in MCL pathogenesis. Results 66 miRs (11 over-expressed, 55 under-expressed) were differentially expressed between MCL and aggressive B-cell NHL and 8 miRs (7 over-expressed, 1 under-expressed) were differentially expressed between MCL and indolent B-cell NHL (false discovery rate = 0.2). 6 miRs from each group were chosen for validation in an independent set of MCL and NHL cases. Of these 12 miRs, 7 miRs validated (2 were under-expressed in MCL relative to aggressive B-cell NHL, and 5 were over-expressed in MCL relative to indolent B-cell NHL). Genes and pathways involved in disease pathogenesis are most likely targeted by multiple miRs. We thus determined a set of 123 genes predicted to be targets of this MCL miR signature, based on five miR target prediction databases from the mirDIP (microRNA data integration) portal. These genes were significantly enriched for focal adhesion and integrin signalling, proteasome-mediated degradation, and the PI3K signalling pathway. Conclusions Using the largest set of MCL cases evaluated to date, a 7-miR signature characteristic of MCL was discovered. The gene targets of these miRs are enriched for roles in proteasome-mediated protein degradation, consistent with the reported sensitivity of MCL to proteasome inhibitors. In addition, these miRs are predicted to be involved in regulation of PI3K/AKT signalling, confirming reports of the importance of this pathway in MCL pathogenesis. Enrichment of target genes involved in focal adhesion and integrin signalling indicate the importance of MCL-stromal interactions and motivates further study into the role of the tumor microenvironment in MCL pathogenesis. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 4630 Persistence of a mass after first-line treatment is a common problem in nodular sclerosis Hodgkin lymphoma (NSHL). Up to 64% of patients demonstrate residual abnormalities on computed tomography (CT) after therapy, but only 42% of those patients will relapse on follow-up. This is primarily caused by the inability of CT to distinguish viable tumor tissue from fibrosis. Clinicians are faced with the dilemma of whether to pursue second-line treatment for a mass that may be simply scar tissue. The ability to predict which patients are at higher risk for residual mass following curative treatment can aid in the planning of follow-up imaging modalities such as positron emission tomography (PET) scanning which can map out metabolically active tissue (i.e. tumor versus fibrosis) and the need for biopsy of a residual mass. This study was designed to test the hypothesis that the presence of abundant fibrosis in the initial biopsy predicts the presence of residual, post-therapy masses composed primarily of fibrotic tissue. Subjects were consecutive NSHL patients from the years 1996 to 2007 identified from our institution based on the availability of histology slides from the initial diagnostic biopsy, clinical follow-up data, and the results of post-treatment imaging investigations. The initial biopsies were reviewed by a lymphoma pathologist and resident without knowledge of the residual mass status. The proportion of the tissue consisting of fibrous material was graded as a percentage of the total biopsy tissue. The clinical charts were reviewed for baseline patient characteristics, cancer stage and the presence of a residual mass on CT scan 6 months after treatment. Of the 47 subjects included in the study, 25 had residual masses and 22 had none. Patients with increased fibrosis on initial biopsy were significantly more likely to have a residual mass after initial therapy (p=0.028). The degree of fibrosis was independent of gender, stage, and Hasenclever score. Degree of fibrosis was the only factor that was predictive of the presence of a residual mass. Of the 16 patients with residual masses with follow-up Gallium imaging, the result of the scan was more likely to be negative (indicating that the mass is not metabolically active) for patients with a high grade of initial fibrosis (p=0.148). Taken together, these results suggest that patients with increased fibrosis on their initial NSHL biopsy are more likely to have residual masses, but that these masses are less likely to be malignant. The results support the hypothesis that the degree of fibrosis at the initial NSHL biopsy is predictive of a post-treatment residual mass. These findings have potential implications for patient follow-up: clinicians whose patients have abundant fibrosis at initial biopsy may be reassured that a post-treatment residual mass is less likely to represent persistent malignancy and thus can be followed with functional imaging rather than pursuing unnecessary biopsies. Our results further reinforce the importance of functional imaging like PET, particularly in this patient population Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 800 Mantle cell lymphoma (MCL) is a B-cell non-Hodgkin lymphoma (NHL) accounting for ~6% of all NHL. It is sensitive to combination chemotherapy, but remission durations are short without approaches such as stem cell transplantation (SCT). Most patients are incurable, but the clinical course is variable, with some patients succumbing quickly, while others survive 〉10 years. MicroRNAs (miRs) are small, non-coding RNAs that regulate gene expression by inhibiting mRNA translation. miRs are useful in the prognostic assessment of tumors, but work to date examining differences between MCL and normal lymphoid tissues, have only identified 2 miRs involved in MCL prognosis (Zhao JJ, Blood, 2010; Di Lisio L, Leukemia, 2010). We used a novel approach to identify a prognostic miR signature in MCL. We hypothesized that a miR signature defining aggressiveness can be obtained by comparing miR expression profiles of aggressive NHL with indolent NHL, and that this signature when applied to a set of MCL cases, may aid in MCL prognosis. Total RNA was extracted from 135 formalin-fixed paraffin-embedded samples obtained at primary diagnosis (Table 1). RNA from a training set of 19 indolent and 20 aggressive NHL cases was analyzed on a high-throughput quantitative real-time PCR (qRT-PCR) platform assessing the expression of 365 miRs and 3 endogenous controls (TaqMan Human MicroRNA Array v1.0: TLDA, ABI) using the DDCt method. A two-sample Wilcoxon Rank sum test corrected for false discovery rate was used to assess the significance of differential expression for each miR between aggressive and indolent NHL. The 14 most significantly differentially expressed miRs (p

Description: Background: Vascular anomalies are diverse entities and can range in severity from self-limiting to life-threatening. Diagnosis and care of these patients is challenging due to overlapping clinical and histologic features. Recently, it has been established that many vascular anomalies arise from somatic mutations in cancer genes (PIK3CA, AKT, NRAS). Use of cancer genomics in patients with vascular anomalies may establish a genetic diagnosis and expand use of targeted medical therapies. We evaluated the utility of targeted next generation sequencing for vascular anomalies patients at a single pediatric center. Methods: Using OncoPanel, a hybrid-capture and massively parallel sequencing assay that surveys DNA sequences of 447 genes implicated in cancer, we analyzed genetic variants in lesional tissue from vascular anomalies patients evaluated at Boston Children's Hospital between 5/2/2017 and 3/23/2020. Results: A total of 276 patients were consented and sequenced under the Dana Farber Cancer Institute Profile protocols DFCI 11-104 (n= 68) and DFCI 17-000 (n= 208). Clinical diagnoses prior to testing were varied and 11 patients (7%) had an unknown diagnosis. Tissue was analyzed for 138 patients. Targeted sequencing resulted in diagnostically significant alterations in 80 of 138 (57%) of patients and therapeutically significant alterations in 58 of 138 (42%) patients. To date, 18 patients in our cohort have been treated with medical therapy informed by their genetic diagnosis. Several more await enrollment on clinical trials. For patients with diagnoses previously categorized as unknown (n=11), sequencing led to identification of a genetic variant in 6 patients (54%). Additionally, 8/138 patients had variants requiring further evaluation for potential germline involvement. Discussion: Next generation sequencing in vascular anomalies patients identified actionable variants in a large proportion of the patients in our cohort. The mTOR inhibitor sirolimus has been used to treat a variety of vascular anomalies, but not all patients respond to this treatment. Targeted therapies based on specific genotypes hold promise as clinical trials in vascular anomalies are emerging. Additionally, sequencing in this cohort identified several variants suggesting a germline cancer predisposition requiring follow-up. Use of next generation sequencing has clinical utility and increased use of this testing may improve diagnosis, prognosis, and treatment for patients with vascular anomalies. Disclosures Adams: Novartis: Consultancy; Venthura: Consultancy. OffLabel Disclosure: Sirolimus is used off-label for the treatment of vascular anomalies.