Citations

Abstract Background: Cyclin dependent 4/6 kinase inhibitors (CDK4/6i) and endocrine therapy (ET) have improved progression-free survival (PFS) and overall survival in hormone-receptor (HR)-positive metastatic breast cancer (MBC), but progression of disease is inevitable. Serum thymidine kinase-1 (TK1) is a secreted marker of proliferation that is prognostic in patients (pts) with HR-positive, HER2-negative MBC and may be predictive of ET and CDK 4/6i response. PROMISE (NCT0281902) is a prospective study enrolling women with HR-positive MBC starting palbociclib (Pb) + letrozole (L) (1st line) or Pb + fulvestrant (2nd line). We undertook a comprehensive “omic” assessment of blood, tumor, urine and the fecal microbiome in order to identify novel genomic variants and pathways associated with an early decline in TK1 (measured after 2 months) and PFS. Additionally, patient derived xenografts/organoids were generated at baseline and progression to test new therapeutic approaches to overcome resistance to CDK4/6i and ET. We report the initial association between the baseline genomic landscape and baseline TK1 levels. Methods: FFPE tumor biopsies were obtained for DNA/RNA sequencing (TempusTM) and blood samples for TK1 (Divitum® assay, Biovica) were collected pretreatment (pre-Pb) and after 2 cycles of Pb + ET (post-Pb2). Both whole-exome (exome capture) sequencing (WES) and RNA-Seq used the Integrated DNA Technologies xGen Exome Research Panel v1.0 capture kit. TK1+ disease was defined as > 200 Du/L and TK1- disease as below limit of detection up to 200 Du/L. We tested the association between genomic and transcriptomic characteristics with baseline TK1 data in pretreatment samples where both WES and RNA-seq and TK1 was available. The data were analyzed using bioinformatics pipelines for somatic and germline mutations and copy number alterations. The current analysis focuses on baseline 1st-line pre-Pb omics data in conjunction with baseline TK1 levels. The database was locked for analysis on 5/29/2020. Results: Thirty-three pts (median age: 59 yrs.) were evaluable, with paired samples for TK1 in 32. Six pts had TK1+ disease pre-Pb and post-Pb2. Twenty-two pts had TK1- disease pre-Pb and post-Pb2. Four pts had a decrease in TK1 after 2 cycles of treatment that altered the classification from TK1+ to TK1-. Both baseline RNA seq and serum TK1 (n=16) were available for 4 TK1+ and 12 TK1- pts. In this group, 476 genes were differentially regulated (398 upregulated; 78 downregulated). Pathway analysis demonstrated enrichment in complement and coagulation cascade pathway, PPAR signaling pathway, and metabolism-related pathways related to up-regulation of CYP and UGT gene families. Further testing for the association of WES data with baseline TK1+ (n=8) and TK1- (n=16) disease demonstrated somatic copy number variations on chromosomes 6, 11, 12 and 15. CDK4 copy number gains were observed in 3/8 TK1+ pts and 0/16 TK1- pts. We also observed that somatic mutations (LOH, copy number and/or SNV/INDELs) were more prevalent in the TK1+ compared to the TK1- pre-Pb group in several cancer-associated genes (FAS [p=0.06] PTEN, PIK3CB, NAB2, SOX9 and FAT1 [p=0.08], TP53, and MAP2K4 [p=0.22]). Conversely, we also noted that 6/7 pts with GATA3 mutations had TK1- disease (p=0.23). Conclusions: Using a comprehensive “omics” approach, our data suggest that a secreted biomarker of proliferation (TK1) obtained prior to initiating CDK4/6i and ET for the first line treatment of HR+ MBC is associated with established and novel genes and pathways associated with prognosis of pts receiving ET and CDK 4/6i. Analysis of on-treatment (after 2 cycles) tumor RNA seq and its association with change in TK1 as well as data from the 2nd-line cohort will be presented at the meeting. Citation Format: Ciara C O Sullivan, Krishna R Kalari, Vera J Suman, Peter T Vedell, Ann Moyer, Abraham D Eyman Casey, Jason Sinnwell, Xiaojia Tang, Kevin Thompson, Alvaro Moreno-Aspitia, Donald W Northfelt, Minetta C Liu, Tufia C Haddad, Saranya Chumsri, Prema Peethambaram, Kathryn J Ruddy, Karthik V Giridhar, Roberto A Leon-Ferre, Adrian Nordmark, Mattias Bergqvist, Brendan P McMenomy, Richard M Weinshilboum, Liewei Wang, Matthew P Goetz. Novel genomic variants and pathways associated with baseline serum thymidine kinase 1 levels in HR-positive HER2-negative MBC patients commencing palbociclib and letrozole [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 PS5-24.

Abstract Background: Patient derived xenografts are a standard tool used to study cancer biology and evaluate drug response phenotypes. It is well known that PDX take rate is associated with more aggressive clinical features [higher grade, biologic subtype (e.g. TNBC vs luminal)]. Previous data from a small retrospective cohort of patients (pts) with no prior chemo (n=24) suggested that primary breast tumor PDX take rate was associated with reduced overall survival. (Derose Nat Med. 2011) However, whether take rate is prognostic in newly diagnosed pts receiving standard of care neoadjuvant chemotherapy (NAC) is unknown. From the prospective BEAUTY clinical trial of pts treated with NAC in which PDX was attempted from pre-NAC as well as after chemo (post-NAC), we recently reported no difference in take rate comparing pts with or without a pathologic complete response (pCR) (Yu Breast Canc Res 2018). Herein we report the association between PDX take rate and recurrence from tumor samples implanted pre-NAC as well as post-NAC (time of surgery). Methods: The BEAUTY study is a prospective NAC study which enrolled breast cancer pts (Stage I-III; n=140) treated with neoadjuvant weekly taxane +/-trastuzumab followed by anthracycline-based chemotherapy. Percutaneous tumor biopsies were obtained prior to NAC and tumor samples from residual disease at surgery were additionally used to establish PDXs. Tumor take rate was defined as percent of pts with the development of at least one stably transplantable (passed at least for four generations) xenograft that was pathologically confirmed as breast cancer. Time to breast cancer recurrence was defined as the time from surgery to documentation of a local, regional, or distant recurrence. Gray’s test was used to assess whether the cumulative incidence (CI) of a breast cancer recurrence differs with respect to either pre-NAC PDX take or post-NAC PDX take. Results: Of 140 pts enrolled in the BEAUTY study, tumor tissue for PDX from the pre-NAC tumor was available for implantation in 113. As previously published, PDX take rate from pre-NAC tumor was 27.4% (31/113), and varied according to tumor clinical subtype [51.3% (20/39) in triple negative breast cancer (TNBC), 26.5% (9/34) in HER2+, 5.0% (2/40) in Luminal]. With median follow up of 5.7 years (range: 3 months to 6.75 years), 17 pts developed local, regional or distant disease relapse (4 of whom had a PDX established pre-NAC). The cumulative incidence of breast cancer relapse after surgery was not found to differ according to pre-NAC PDX take (5 yr CI rate: 13.6% no take; 13.4% take; p=0.8911). In pts with TNBC, the group with the highest take rate, there was also no significant difference in incidence of BC recurrence between those without PDX take and those with PDX take (5 yr CI rate: 21.4% vs 16.2% p=0.7314). PDXs were established from residual tissue from surgery (post-NAC) in 6 of 34 pts (17.6%), [specifically, TNBC: 5/9; Her2+: 1/8; and Luminal: 0/17]. Nine of these 34 pts developed a local, regional or distant recurrence. There was a tendency for pts who had a PDX established from their residual disease to have a higher incidence of a breast event (p=0.1092). The 5 year cumulative incidence of a breast event was 19.6% for pts whose post-NAC PDX did not take and 50.0% for pts whose post-NAC PDX took. Discussion: In pts receiving NAC for breast cancer, we observed no significant difference between establishment of a pre-NAC PDX and breast cancer relapse. In contrast, post-NAC PDX take rate (from residual tumor obtained from the breast at surgery) was associated with a tendency to have a higher incidence of a breast cancer event. PDXs remain a valuable tool for the evaluation of tumor biology and development of new therapeutics, especially those models established from pts with chemotherapy resistance. Citation Format: Judy C. Boughey, Vera J. Suman, Jia Yu, Katelyn Santo, Jason P. Sinnwell, Jodi M. Carter, Krishna R. Kalari, Xiaojia Tang, Sarah A. McLaughlin, Alvaro Moreno Aspitia, John A. Copland, III, Donald W. Northfelt, Richard J. Gray, Katie N. Hunt, Amy Lynn Conners, Richard Weinshilboum, Liewei Wang, Matthew P. Goetz. Association between patient derived xenograft (PDX) take rate and breast cancer recurrence in the prospective breast cancer genome guided therapy study (BEAUTY) [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 PD7-04.

Because up to 12% of obstetric patients meet criteria for the diagnosis of thrombocytopenia in pregnancy, it is not infrequent that the anesthesiologist must decide whether to proceed with a neuraxial procedure in an affected patient. Given the potential morbidity associated with general anesthesia for cesarean delivery, thoughtful consideration of which patients with thrombocytopenia are likely to have an increased risk of spinal epidural hematoma with neuraxial procedures, and when these risks outweigh the relative benefits is important to consider and to inform shared decision making with patients. Because there are substantial risks associated with withholding a neuraxial analgesic/anesthetic procedure in obstetric patients, every effort should be made to perform a bleeding history assessment and determine the thrombocytopenia etiology before admission for delivery. Whereas multiple other professional societies (obstetric, interventional pain, and hematologic) have published guidelines addressing platelet thresholds for safe neuraxial procedures, the US anesthesia professional societies have been silent on this topic. Despite a paucity of high-quality data, there are now meta-analyses that provide better estimations of risks. An interdisciplinary taskforce was convened to unite the relevant professional societies, synthesize the data, and provide a practical decision algorithm to help inform risk-benefit discussions and shared decision making with patients. Through a systematic review and modified Delphi process, the taskforce concluded that the best available evidence indicates the risk of spinal epidural hematoma associated with a platelet count ≥70,000 × 10 6 /L is likely to be very low in obstetric patients with thrombocytopenia secondary to gestational thrombocytopenia, immune thrombocytopenia (ITP), and hypertensive disorders of pregnancy in the absence of other risk factors. Ultimately, the decision of whether to proceed with a neuraxial procedure in an obstetric patient with thrombocytopenia occurs within a clinical context. Potentially relevant factors include, but are not limited to, patient comorbidities, obstetric risk factors, airway examination, available airway equipment, risk of general anesthesia, and patient preference.

Abstract Context. —Pituitary adenomas are clinically diagnosed based on radiologic studies and/or secondary effects of hormone production. Definitive pathologic identification relies on immunohistochemical detection of a clonal population of hormone-producing cells. However, not all adenomas secrete hormones, so performing a battery of stains is inefficient. Reports have shown decreased type IV collagen in the stroma of other epithelial tumors. Objective. —To validate type IV collagen immunohistochemistry as a diagnostic method. Design. —We immunostained 27 adenomas and 19 normal pituitaries. The areas with the sparsest type IV collagen fibers were viewed at 3 magnifications (×10, ×20, and ×40 objectives), counting 1, 3, or 10 microscopic fields. A field was scored as “traversable” if a path existed from any point on the periphery of the field to a point on the approximately opposite periphery that did not cross any stained fibers. Results were compared with reticulin staining and to the existing diagnosis previously determined by histology, hormone immunostaining, and clinical correlation. Results. —Adenomas have less type IV collagen in their basement membranes, leading to sparser, trabecular staining in neoplasms versus a more rigid meshwork pattern in normal glands. One might envision the stained fibers as maze walls—one can traverse medium-powered fields in an adenoma, but one hits dead ends and gets trapped in those of a normal gland. Finding a single representative ×10 field to be traversable was 97.5% sensitive and 96.5% specific for an adenoma. Reticulin staining yielded identical results. Conclusions. —Type IV collagen immunostaining is a simple and reliable method of diagnosing pituitary adenomas.

Abstract Funding Acknowledgements Type of funding sources: None. BACKGROUND Detection of immobile leaflets immediately following bioprosthetic valve implantation is a rare but important intraoperative finding. Restriction of leaflet movement can occur in the closed or open position, leading to abnormal prosthesis function. We sought to determine the clinical implications of immobile leaflets seen on intraoperative echocardiography. METHODS Patients with immobile leaflets identified on intra-operative/procedure echocardiography immediately post implantation between 2009-2020 were identified from an institutional database. All echocardiograms were reviewed de-novo to confirm immobile leaflets in the immediate post-implantation period. Identified cases were matched 1:2 to controls for age; sex; prosthesis position, model and size; and implantation approach (surgical vs. transcatheter). Nominal logistic regression and proportional hazards were used to analyze outcomes. RESULTS Thirty patients with immobile leaflets immediately post-bioprosthesis implantation were included. Clinical characteristics are summarized in the Table. Immobile leaflets were documented in procedural reports in only 18 (60%) patients. Moderate stenosis was present intraoperatively in 1 patient, none demonstrated ≥moderate regurgitation, and none resulted in immediate corrective action. In 3 (10%), valve re-intervention was required within 30 days due to symptomatic prosthesis dysfunction. Presence of restricted leaflet motion was associated with higher need for post-operative extracorporeal membrane oxygenation use (odds-ratio 7.3, p = 0.02) and composite end-point of death, valve re-replacement, prosthesis thrombosis, or cardiac hospitalizations (risk ratio 2.1, p = 0.03, Figure). CONCLUSION Immobile leaflet(s) immediately post-bioprosthetic valve implantation is an uncommon, under-reported, and under-treated phenomenon. Even in the absence of significant prosthetic valve dysfunction, it can be associated with worse post-operative course as well as worse outcomes. Baseline characteristics Age 76 (67-84) Sex, male 10 (33%) Surgical approach 25 (83%) Aortic 5 (17%) Mitral 12 (40%) Tricuspid 12 (40%) Pulmonary 1 (3%) Re-intervention within 10 days 3 (10%) Numbers are presented as median (interquartile range) or number (percentage). Abstract Figure. Clinical outcome of stuck leaflets

Abstract Purpose Recent advances in molecular diagnostic technologies allow for the evaluation of solid tumor malignancies through noninvasive blood sampling, including circulating tumor DNA profiling (ctDNA). Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis, often because of late presentation of disease. Diagnosis is often made using endoscopic ultrasound or endoscopic retrograde cholangiopancreatography, which often does not yield enough tissue for next-generation sequencing. With this study, we sought to characterize the ctDNA genomic alteration landscape in patients with advanced PDAC with a focus on actionable findings. Materials and Methods From December 2014 through October 2019, 357 samples collected from 282 patients with PDAC at Mayo Clinic underwent ctDNA testing using a clinically available assay. The majority of samples were tested using the 73-gene panel which includes somatic genomic targets, including complete or critical exon coverage in 30 and 40 genes, respectively, and in some, amplifications, fusions, and indels. Clinical data and outcome variables were available for 165 patients; with 104 patients at initial presentation. Results All patients included in this study had locally advanced or metastatic PDAC. Samples having at least one alteration, when variants of unknown significance (VUS) were excluded, numbered 266 (75%). After excluding VUS, therapeutically relevant alterations were observed in 170 (48%) of the total 357 cohort, including KRAS (G12C), EGFR, ATM, MYC, BRCA, PIK3CA, and BRAF mutations. KRAS, SMAD, CCND2, or TP53 alterations were seen in higher frequency in patients with advanced disease. Conclusion Our study is the largest cohort to date that demonstrates the feasibility of ctDNA testing in PDAC. We provide a benchmark landscape upon which the field can continue to grow. Future applications may include use of ctDNA to guide treatment and serial monitoring of ctDNA during disease course to identify novel therapeutic targets for improved prognosis. Implications for Practice Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis often due to late presentation of disease. Biopsy tissue sampling is invasive and samples are often inadequate, requiring repeated invasive procedures and delays in treatment. Noninvasive methods to identify PDAC early in its course may improve prognosis in PDAC. Using ctDNA, targetable genes can be identified and used for treatment.

Hematological malignancies comprise a genetically heterogeneous spectrum of diseases caused by abnormal proliferation or maturation of a variety of hematological cell lineages. Genomic abnormalities including chromosomal translocations, copy number variations and sequence level gene mutations underlie the pathogenesis of these disorders and frequently serve as important diagnostic, prognostic and/or therapeutic markers. However, the substantial discrepancy in interpretation and reporting of these genomic abnormalities among testing labs creates challenges for patient management. Therefore, standardizing the curation, clinical interpretation and reporting of somatic alterations within the context of their diagnostic, prognostic and therapeutic significance in hematological cancers is critical. In January 2020, the ClinGen Somatic Cancer Clinical Domain working group formed the Hematological Cancer Taskforce (HCT) with a goal to undertake systematic curation and evidence-based clinical interpretation of genes/somatic variants associated with hematological malignancies. The HCT has recruited 32 multi-disciplinary experts including oncologists, molecular pathologists, clinical lab directors, genomic scientists and biocurators with expertise in hematological malignancies. In collaboration with the Clinical Interpretation of Variants in Cancer (CIViC) (civicdb.org) knowledgebase, variants from peer-reviewed publications are curated with editor review for clinical utility as evidence items. Monthly discussions based on these evidence items lead to the creation of summary variant assertions using the AMP/ASCO/CAP guidelines (Li M, et al., Journal of Molecular Diagnostics, 2017). The HCT is currently focused on expert curation and clinical interpretation of somatic variants in FLT3 (internal tandem duplication, tyrosine kinase domain and non tyrosine kinase domain variants) in acute myeloid leukemia (AML). Expert curation of gene fusions in Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) in collaboration with the ClinGen somatic pediatric cancer taskforce is currently underway. To date, the HCT has curated 45 evidence items from clinical and pre-clinical studies on the aforementioned genes/variants. In addition, three AMP Tier I, level A variant assertions of FLT3-ITD, D835 and I836, which predict response to Gilteritinib, an FDA-approved drug for relapsed or refractory AML, have been curated. In the future, the HCT plans to extend its focus on curation of BCR-ABL1 kinase domain mutations in chronic myeloid leukemia (CML). Based on the initial pilot curation phase, the HCT will develop gene-specific recommendations to standardize the reporting and interpretation of somatic variants to better assist clinical decisions and apply to become official ClinGen Somatic Expert Panels in each of these gene-disease domains. Disclosures Blombery: Novartis: Consultancy; Invivoscribe: Honoraria; Amgen: Consultancy; Janssen: Honoraria.

Background: Subcutaneous lymphomas are a heterogeneous group of diseases with variable clinical behavior that ranges from a lymphoproliferative disorder to an aggressive cytotoxic lymphoma. Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is an uncommon, often indolent cutaneous lymphoma that localizes to the subcutaneous adipose tissue. These tumors exhibit an alpha/beta phenotype (abSPTCL). Primary cutaneous gamma-delta T-cell lymphoma (PCgdTCL) is a rare, highly aggressive lymphoma that frequently involves the subcutaneous adipose tissue. The goal of this study is to identify key inflammatory and oncogenic pathways in SPTCL and PCgdTCL to determine which mutational or expression patterns differentiate abSPTCL and PCgdTCL. A comprehensive catalog of cancer gene expression profiles generated via RNA sequencing on patient samples is essential to understand tumorigenesis and to develop effective therapies. Methods: We performed transcriptomic profiling analysis using RNA sequencing in lesional skin biopsies from patients of abSPTCL (n=10), PCgdTCL (n=9), and controls (n=5). Differential analyses were performed on the entire transcriptomic profiles among the 3 groups. Results: Although the transcriptomic profiles of abSPTCL and PCgdTCL samples had similarities, there were notable differences between these groups that may elucidate unique pathways that propagate each disease. In contrast to abSPTCL, PCgdTCL samples demonstrated upregulation of cell motility and proliferation, and downregulation of pathways involving apoptosis and tumor necrosis factor production. The most significantly upregulated gene pathways in both abSPTCL and PCgdTCL samples were those involving immune and inflammatory response, viral defense, type I interferon signaling, interferon-gamma-mediated signaling, and positive regulation of T cell proliferation. The most significantly downregulated gene pathways in the two groups were those involving cell adhesion, rRNA processing and translation, and extracellular matrix organization. The top 5 upregulated immune response and downregulated cell adhesion hub genes for abSPTCL highlighted by gene interaction network analysis included: TNF, CTLA4, CD86, IL10, CCR5 & ITGB5, ITGA8, VWF, APP, CDH5, respectively. Conclusion: Our transcriptomic profiling pinpoints disease-related enrichment pathways and gene functions in abSPTCL and PCgdTCL patients, which may shed light on molecular mechanisms that drive disease activity. Hub genes in abSPTCL represent potential drug targets for further development of novel therapies. Disclosures Mangold: Kirin:Membership on an entity's Board of Directors or advisory committees;Elorac:Research Funding;Sun Pharma:Research Funding;MiRagen:Research Funding;Solagenix:Research Funding.

Background: Infection during the period of neutropenia following chemotherapy represents a major cause of morbidity and mortality in patients with malignancy.(Freifeld, et al, 2011, Baden LR, et al, 2012) Several guidelines recommend granulocyte colony stimulating factor (GCSF) to reduce the duration and severity of chemotherapy-induced neutropenia and abate infection risk.(Lyman, et al 2018, Aapro, et al, 2011, Smith, et al, 2015). Optimal GCSF administration following chimeric antigen receptor (CAR) T-cell therapy remains undefined and requires characterization. Methods: The Mayo Institutional Review Board approved this retrospective, single-center study. Electronic medical records for patients prescribed axicabtagene ciloleucel were reviewed until disease relapse, death, or a maximum of 60 days after infusion. Baseline characteristics and laboratory values were abstracted prior to lymphodepleting chemotherapy. GCSF support was originally prescribed when the absolute neutrophil count (ANC) declined below 500 cells/mm3 and discontinued when the ANC exceeded 1000 cells/mm3 (neutropenia) for 2 consecutive days. A practice change was made where GCSF was recommended only in those with febrile neutropenia and an increased concern for infection. The primary endpoint was the difference in the total days of neutropenia for patients receiving and not receiving GCSF. Secondary outcomes compared total days of severe neutropenia, number of neutropenia episodes, infection rates by GCSF use, and outcomes by protocol change. Neutropenia and severe neutropenia were defined as an ANC below 500 cells/mm3 and 100 cells/mm3, respectively. Updated data with more patients will be presented at the conference. Results: The 60 included patients had a median age of 59 (IQR: 44, 63) years, 38 (63%) were male and 53 (88%) were Caucasian. Significantly fewer patients were prescribed GCSF according to infection-related concerns compared to ANC-based indication, 18% vs. 94%, p<0.001. Because only 3 subjects received GCSF based on infection-related concerns, results based on GCSF use versus no use is shown here. GCSF was prescribed to 35 (58%) patients for a median of 8 (IQR: 6, 12) doses with a median cumulative dosage of 3840 mcg (IQR 2100-5400) and median time to first dose of 3 days (IQR: 1, 4) post CAR T-cell infusion. Table 1 displays additional baseline characteristics and laboratory parameters according to GCSF support utilization. GCSF prescribed: Table 2 displays outcomes by GCSF use. Total days of neutropenia were similar between groups (13 vs. 16, p=0.52) with a trend towards significantly fewer days of severe neutropenia when prescribed GCSF (6 vs. 9, p=0.129). Patients prescribed GCSF were more likely to experience multiple episodes of neutropenia (83% vs. 43% p=0.002) with a significantly greater median number of episodes (3 vs. 1, p=0.002) when compared to those not prescribed GCSF. GCSF use significantly decreased the median days of the first neutropenia episode (6 vs. 12, p=0.001). There was a trend for decreased median days of severe neutropenia in the first episode with GCSF (5.0 vs. 8.0, p=0.236). Figure 1 displays a trend towards a lower overall risk of infection (HR 0.55, 95%CI: 0.16-1.87, p=0.34) and lower risk of bacterial infection (HR: 0.49, 95% CI: 0.18-1.31, p=0.15); however, these were not statistically significant. Conclusion: Patients prescribed GCSF according to ANC-based indication were significantly more likely to experience multiple neutropenia episodes; however, duration of first neutropenic episode and days of severe neutropenia during the first neutropenic episode were significantly reduced. Interestingly, the total days of neutropenia and severe neutropenia were similar between groups. It is possible that using the parameter of ANC more than 1000 cells/mm3 for 2 consecutive days is not the optimal criteria for stopping GCSF. Risk of overall and bacterial infection was lower with ANC-based initiation of GCSF, although non-significant likely due to small sample size. The potential benefit for using CSF and the optimal timing after CAR T-cell infusion requires further, rigorous, prospective investigation. Disclosures Ansell: ADC Therapeutics: Research Funding; Trillium: Research Funding; Affimed: Research Funding; Regeneron: Research Funding; AI Therapeutics: Research Funding; Takeda: Research Funding; Seattle Genetics: Research Funding; Bristol Myers Squibb: Research Funding. Bennani:Purdue Pharma: Other: Advisory Board; Kite/Gilead: Research Funding; Affimed: Research Funding; Verastem: Other: Advisory Board. Lin:Kite, a Gilead Company: Consultancy, Research Funding; Vineti: Consultancy; Sorrento: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gamida Cells: Consultancy; Takeda: Research Funding; Merck: Research Funding; Legend BioTech: Consultancy; Juno: Consultancy; Bluebird Bio: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Janssen: Consultancy, Research Funding.