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Introduction: Lymphodepletion (LD) chemotherapy is critical for the efficacy of CAR-T therapy by eradicating immunosuppressive cells, inducing costimulatory molecules, and promoting expansion and persistence of CAR-T cells. It also can contribute to an increased risk of infections, cytopenia, and other toxicities. We evaluated the utilization of varying LD regimens used in standard-of-care (SOC) autologous B-cell maturation antigen-directed (BCMA) CAR-T therapy with ide-cel or cilta-cel for relapsed/refractory multiple myeloma (RRMM) and the effect on outcomes and toxicity. Methods: Data were retrospectively collected from patients with RRMM who underwent LD and CAR-T cell infusion by December 31, 2022, from 13 US academic institutions with SOC ide-cel or cilta-cel. Response rates and other categorical variables, specifically LD regimen, were tested for association using Wilcoxon rank-sum (or Kruskal-Wallis for three or more groups) or Fisher's exact tests, respectively. Results: A total of 523 patients were infused at the time of data cut-off with 489 patients evaluable for safety and survival analyses; 368 (75%) were infused with ide-cel and 121 (25%) with cilta-cel. The median age was 65 years old (range 30-90) with 206 females (42%) and 283 males (58%), and 13% with ECOG performance status ≥ 2 at time of LD. Fludarabine and cyclophosphamide (Flu/Cy) LD was used in 422 patients while 67 patients received other LD regimens including bendamustine-based (n = 35, 52%), cladribine-based (n = 25, 37%) or cyclophosphamide alone (n = 7, 10%). The primary reason for use of Flu/Cy LD was institutional guidance or SOC in 378 patients (90%), while the primary reason for use of other LD regimens was due to the fludarabine shortage in 65 patients (97%) with 3% citing physician's choice or institutional guidance. No significant difference was identified among response outcomes, with those receiving Flu/Cy LD achieving an ORR of 84% compared to 81% with other LD regimens (p = 0.59) and no difference observed in rates of ≥ VGPR (66% Flu/Cy LD vs 60% other LD; p = 0.48). Of those evaluable for MRD at 1 and 3 months, the MRD negative rate at 10 -6 for those with Flu/Cy LD was 77% (n= 137) and 77% (n=113) and with other LD regimens was 66% (n=35) and 79% (n=28), respectively. At a median follow-up of 9.7 months, no statistically significant difference was noted in median progression free survival (mPFS) with Flu/Cy vs other LD regimens (9.3 mos vs NR) or overall survival (OS) (19.4 mos vs NR). When stratified by type of CAR-T therapy, treatment with bendamustine-based LD was associated with an inferior mPFS compared to those receiving Flu/Cy LD in patients treated with ide-cel (3.8 vs 8.5 mos; p=0.0056), though not by multivariate analysis. Univariate analysis of patients treated with ide-cel between Flu/Cy and bendamustine LD did not reveal any significant differences in age, gender, ECOG, R-ISS stage, extramedullary disease, high-risk cytogenetics or renal dysfunction (Cr < 45 ml/min). LD regimen was not a predictor for PFS on multivariable analyses amongst patients treated with ide-cel, while ECOG ≥ 3 (hazard ratio [HR]= 4.44, 95% confidence interval [CI]= 1.40, 14.08) and t(4,14) (HR= 2.02, 95% CI=1.14, 3.59) were associated with worse PFS. No difference in mPFS by LD regimen was observed in patients receiving cilta-cel, which was a smaller cohort (mPFS: Flu/Cy 11.7 mos, bendamustine-based NR, cladribine-based NR, cyclophosphamide NR). Rates of all grade CRS (81% vs 70%), Grade ≥ 3 CRS (3% vs 3%), all grade ICANS (19% vs 12%, and Grade ≥ 3 ICANS (4% vs 2%) were similar among those receiving Flu/Cy or other LD regimens, respectively. Patients receiving Flu/Cy LD were less likely to have any grade cytopenia at 1 month (33% vs 55%, p < 0.001) and 3 months (52% vs 69%, p < 0.001), with no observed difference in infection rate. Conclusions: The fludarabine shortage experienced in the US in late 2022 necessitated the use of alternative LD regimens with BCMA-directed CAR-T therapy with most centers relying on bendamustine- or cladribine-based regimens. Use of bendamustine-based LD was associated with inferior PFS in patients receiving ide-cel on univariate analysis, but not on multivariate analysis after adjusting for other prognostic factors. In summary, there is no clear difference in efficacy or safety between Flu/Cy and non-Flu/Cy LD in patients receiving BCMA-directed CAR-T therapy. *Authors contributed equally

Introduction: In many cases, treatment decisions for multiple myeloma patients must be made in the absence of high quality randomized controlled clinical trials. As a result, many clinicians lean on prognostic models to drive treatment selection. The most widely used of these models incorporate a limited number of patient related factors that reflect tumor burden, cytogenetic features, or gene expression profiling. These prediction scores are derived from regression models that incorporate these variables at the time of diagnosis. They do not account for variables that change dynamically over time, do not explore the relationship between treatment selection and progression, and imperfectly predict survival outcomes. We designed a prognostic model based on an ensemble machine learning platform to predict progression in NDMM using Extreme Gradient Boosting Machine (XGBoost) combined with accelerated failure time modeling for survival analysis. Methods: We utilized a large retrospective data set containing treatment and response information for 1127 patients with newly diagnosed multiple myeloma (NDMM) treated at the Cleveland Clinic Foundation between 2000 and 2023. Following data preprocessing based on data completeness, 953 patient records were included in our training, testing, and cross validation datasets. For the purposes of our analysis, the initial dataset was randomly split into training (70%), testing (15%) and validation (15%) subsets at the patient level. We also defined the lower and upper bounds for each subset, which is critical due to the right-censored nature of survival data. Hyperparameters for XGBoost were optimized using Bayesian search, minimizing the negative log-likelihood. A random forest method was applied for the imputation of missing data (MissForest). We then trained the XGBoost model using GPU acceleration for enhanced computational efficiency. Finally, a log-rank test on predicted survival times was used to test the model's performance on patients with and without known progression. Results: Our preprocessed data set had 953 patients with a mean age at disease onset of 65 years and a slight male predominance (55%). Approximately 27% of patients harbored high cytogenetic risk disease and 3.5% of the cohort presented with extramedullary disease a diagnosis. At a median follow up of 35 months, 47% of patients had experienced disease progression or death. Induction therapy included an immunomodulatory drug in 40% of patients and proteasome inhibitors in 22%. Frontline autologous stem cell transplantation followed induction in 28% of patients. Median progression free survival in the overall data set was 44 months. These features were consistent across the randomly assigned training, testing, and validation cohorts. Following data preprocessing, 34 independent clinical and genomic variables including selection of first line treatment were assessed as model inputs each available record. Under optimized parameters, the model was trained with a maximum tree depth = 7 and a learning rate ~ 0.22 for the desired output of progression free survival (PFS). We then queried PFS for both the training and validation sets and divided patients into those known to have progressed and those without a progression event. Survival analysis was undertaken using predicted PFS values for patients known to have progressed and those who remained progression free. For the validation data set, our model successfully discerned between progressed and non-progressed cases (log-rank test statistic = 22.07, p < 0.005) (Figure 1). Discussion: We present a machine learning approach based on regularized gradient boosting that accurately discerns between patients who experience progression and those who remain progression free at a median ~35 months of follow-up in a large retrospective data set in patients presenting with NDMM. Further elaboration of our model will allow for the incorporation of large amounts data to predict survival outcomes on the basis of dynamic variables such as depth of response and treatment selection. With the ability to parse outcomes among multiple myeloma patients at high resolution, future clinicians and clinical trialists may be able to overcome limitations in trial design and patient-level therapy selection for both newly diagnosed and relapsed patients.

Introduction: Despite governmental and industry-sponsored efforts, clinical trial participation among rural residents and racial and ethnic minorities remains low. The NIH Revitalization Act of 1993 directed the NIH to establish guidelines for inclusion of women and minorities in clinical research. In 2015, the Food and Drug Administration launched an action plan to improve the quality of demographic subgroup data collection, identify barriers to enrollment, employ strategies to increase participation, and promote transparency of related data. However subsequent studies (Green et al. Health Aff. March 2022, Kanapuru et al. Blood Advances. March 2022.) showed no improvement in participation of racial minorities, including Blacks and Hispanics since this plan was enacted. Various complex system- and individual-based factors, including lack of clinical trial availability; lack of diversity in the investigator work force; scant patient and provider awareness of clinical trials; lack of trust in the health care system; and issues with access to care-often driven by financial, geographic, or social constraints (Allison et al. Cureus. Apr 2022.), and stringent eligibility criteria are deemed responsible. The Leukemia & Lymphoma Society (LLS) IMPACT (Influential Medicine Providing Access to Clinical Trials) research grant strives to bridge this unrelenting care gap. Methods: The LLS IMPACT program includes a 5-year research grant which was launched in 2021. The IMPACT grants support the establishment of clinical trial networks involving academic cancer centers (“Hubs”) linked to community clinics and oncology centers (“Spokes”). The program's overall goal is to provide patients access to trials through participation at the community sites. Initially, 3 institutional sites were selected to participate. These institutions had unique and tailored strategies to improve engagement of underrepresented patients, including black, indigenous, people of color, Hispanic, Latina/Latino, and people from rural communities in vastly different climates and local cultures. The IMPACT grant expanded to encompass 4 additional sites given the imminent needs and clamor of the hematology clinical trials community (Figure 1A). The catchment areas and strategies employed at each institution are summarized in the table (Figure 1B). Results: At the start of the grant period, focus was on building clinical research infrastructure and opening non-interventional clinical trials to teach personnel about clinical research and create relationships with patients. Other programs such as webinar series, tumor boards, technological advancements, and educational workshops were also established to enhance engagement among physicians, match patients to clinical trials, and to provide clinical trial education to potential patients. One trial that has seen early success is the CHIVE IMPACT trial, a non-interventional registry and biorepository which has enrolled 24 patients at a rural and underserved site as of July 2023. The purpose of CHIVE is to enroll patients who have clonal hematopoiesis (CH) or are at risk of CH and follow prospectively in efforts to understand risk of progression and potential for early intervention. The Universal Protocol is another biorepository trial which has more than tripled its enrollment number at a community site between 2021 and 2022. Of the 63 patients enrolled in 2022, 66% of them identified as a race other than White. As our core goal is to increase access to interventional trials, we hope to bring industry sponsored phase II and phase III studies to underrepresented areas that serve a broad patient population. Lack of financial resources, lack of transportation and distance to trial sites, and residual distrust of the medical community (e.g., legacy of Tuskegee experiments) are barriers the grantees are focused on overcoming to enroll the intended populations into clinical trials. Conclusion: The innovative strategies employed to expand access to clinical trials for underrepresented population at the various institutions through the LLS's IMPACT research grant can be utilized during clinical trials design and implementation phases to improve generalizability of clinical trials in hematologic malignancies. In the third year of this program, 7 participating sites are engaging impactful strategies (Figure 1B) which will be reported at the end of the grant period.

Introduction: SystemicAL amyloidosis is a progressive and often fatal disease caused by misfolded light chains that aggregate into amyloid fibrils and deposit in vital organs, leading to organ dysfunction. Current standard of care (SoC) therapies for AL amyloidosis target the plasma cell clone to reduce or eliminate light chain production, but do not remove soluble toxic light chain aggregates or insoluble amyloid deposits. Early mortality remains high for patients with advanced disease (e.g., Mayo 2012 Stage IV disease, median overall survival <6 months). Birtamimab - a humanized monoclonal antibody that neutralizes soluble, toxic light chain aggregates and depletes insoluble amyloid deposits by inducing phagocytosis - is under investigation for the treatment of AL amyloidosis. Here, we present a pooled safety analysis from previous Phase 1-3 clinical trials, with a focus on the 2 double-blind randomized controlled trials (RCTs): PRONTO (NCT02632786) and VITAL (NCT02312206). Methods: Patients with AL amyloidosis were treated with intravenous birtamimab up to 24 mg/kg every 28 daysin the non-placebo-controlled Phase 1/2 open-label trial (NCT01707264) with open-label extension (OLE; NCT02613182) and 2 RCTs (Phase 2 PRONTO with OLE [NCT03154047] and Phase 3 VITAL). In PRONTO, patients had received ≥1 previous systemic therapy with at least a partial hematologic response and persistent cardiac dysfunction, and received birtamimab or placebo. In VITAL, newly diagnosed treatment-naïve patients with cardiac involvement received birtamimab + SoC or placebo + SoC (where SoC was a bortezomib-containing chemotherapy regimen). The analysis included all patients who received ≥1 dose of birtamimab. Pooled median exposure times were calculated, and baseline characteristics and demographics were summarized. For VITAL and PRONTO, pooled rates and severity of treatment-emergent adverse events (TEAEs) with birtamimab were compared with rates in the placebo arms. In addition, safety data from the non-placebo-controlled studies were summarized. Results: The median (range) exposure to birtamimab among 302 patients pooled from the Phase 1-3 trials was 12.24 (0.03-57.72) months. Of the 302 patients exposed to birtamimab, 295 received at least one 24-mg/kg infusion, up to 2500 mg. Analysis of the 2 randomized, placebo-controlled trials included data from 196 patients treated with birtamimab from the PRONTO (n=66) and VITAL (n=130) trials and 193 patients who received placebo (PRONTO, n=63; VITAL, n=130). Both trials had comparable treatment durations overall. The rates of TEAEs, serious and grade ≥3 TEAEs were similar between birtamimab and placebo arms within each trial and between treatment arms in the placebo-controlled pooled analysis set (PRONTO and VITAL; Table 1). Higher rates of treatment-related, serious, and grade ≥3 TEAEs were reported in VITAL compared with PRONTO, presumably due to the treatment-naïve population and receipt of concomitant SoC therapy in VITAL. In the pooled analysis set, the most common TEAEs that occurred with greater frequency in the birtamimab vs placebo arms in either trial were, respectively, fatigue (36.2%, 34.2%), diarrhea (33.2%, 33.7%), nausea (31.6%, 30.1%), constipation (31.1%, 31.6%), and dyspnea (25.0%, 24.9%). The most commonly reported (≥5%) serious and grade ≥3 TEAEs were primarily cardiac disorders (cardiac failure, syncope, cardiac arrest), consistent with the underlying disease. Infusion-associated TEAE rates were low in the pooled birtamimab and placebo arms (5.1% vs 3.6%, respectively) and were generally mild to moderate. The safety profile observed in the non-placebo-controlled Phase 1/2 trial plus OLE and PRONTO OLE (n=106) was consistent with the safety data reported in the placebo-controlled studies. Conclusions: Birtamimab was well tolerated in patients with AL amyloidosis when administered as monotherapy and did not demonstrate additive toxicity when given with SoC chemotherapy. Rates of TEAEs in the birtamimab arm were similar to rates in the placebo arm in the PRONTO and VITAL trials. The safety and efficacy of birtamimab is being further investigated in an ongoing confirmatory Phase 3 double-blind RCT in patients with Mayo Stage IV AL amyloidosis (AFFIRM-AL; NCT04973137), which is currently enrolling.

Abstract Background Cytomegalovirus (CMV) infects millions in the US and is a source of comorbidity among immunocompromised patients. Despite its prevalence, there is limited data on clinical characteristics or outcomes among HIV-negative, non-transplant (NHNT) patients in population-based cohorts. We aim to evaluate a multicenter US-based network to obtain clinical characteristics and outcomes of NHNT patients with CMV disease and explore potential prognostic clinical characteristics implicated in increased morbidity and mortality. Methods This is a US-based multicenter, population-based, retrospective cohort study. We queried TrinetX, a global research network, to identify patients with a CMV disease by ICD-10-CM codes and serum and PCR > 5000 IU/mL. We captured comorbidities diagnosed within 90 days of CMV infection diagnosis, symptoms noted within 30 days, and outcomes of interest at 30 days and 1 year. Primary outcome was all-cause mortality. Secondary outcomes were hospitalization and CMV disease-related complications. We performed a propensity score-matched analysis comparing clinical characteristics among patients who survived versus non-survivors at 90 days. Results We found 1123 patients with evidence of CMV disease. The mean patient age was 53 years, 48% men and 50% white. Aplastic anemia and neoplasms were the most common comorbidities (Table 1). Thromboembolism was a common complication (15%). Half of the patients had dyspnea, fever, abdominal pain, and nausea. CMV disease was associated with 14%, 22%, and 26% mortality at 30 days, 90 days, and one year, respectively. 35% of patients required hospitalization within 30 days. After propensity score matching, we had 278 patients in each cohort. Dyspnea and weakness were linked to increased 90-day mortality (Figure 1). Purpura, encephalopathy, and sepsis were more common in patients who died. High CMV serum viral load and ferritin were associated with increased mortality. Conclusion NHNT patients with CMV disease often have underlying comorbidity, commonly aplastic anemia, and neoplasms. CMV disease was associated with thrombosis and a high risk of hospitalization and mortality. Vascular disease, sepsis, high viral load, and cell lysis markers were prognostic factors for mortality in this cohort. Disclosures Raymund R. Razonable, MD, Allovir: Endpoint Adjudication Committee|American Society of Transplantation: Board Member|Gilead: Grant/Research Support|Novartis: DSMB|Regeneron: Grant/Research Support|Roche: Grant/Research Support

Abstract Background Due to extensive protein binding, use of ceftriaxone in the setting of hypoalbuminemia may result in suboptimal drug exposure via higher concentrations of unbound drug resulting in increased volume of distribution and increased drug clearance. We aimed to evaluate the impact of hypoalbuminemia on clinical success among hospitalized adults with obesity who were treated with ceftriaxone for a bacterial infection. Methods This retrospective review included adult inpatients with weight > 100 kg or body mass index (BMI) > 40 who received ceftriaxone 2 grams intravenously every 12 hours for at least 72 hours for one of the following indications: bloodstream infection, pneumonia, urinary tract infection, non-enterococcal endocarditis, skin and soft tissue infection, or bone and joint infection. The primary outcome was clinical success, a composite of clinical cure and microbiologic cure. Clinical cure was defined as resolution of signs and symptoms compatible with active infection without need to change or extend antibiotic therapy due to inadequate effect of ceftriaxone. Microbiologic cure was defined as negative repeat sterile site cultures, if applicable. Secondary outcomes included length of stay, mortality, and 30-day readmission. Outcomes were analyzed with Mann-Whitney U tests, Pearson’s chi-squared tests, and Fisher’s exact tests (α level = 0.05). Results 137 patients were included, 34 of whom had a serum albumin ≤ 2.5 g/dL. Patients were predominantly white (94.2%) and male (69.3%) with a median BMI of 48.6 (Table 1). Clinical success, a composite of clinical and microbiologic cure, was achieved in 76.5% and 92.2% (p = 0.013) of those with and without hypoalbuminemia, respectively. Clinical cure was significantly more common among those without hypoalbuminemia (93.2%) as compared to those with hypoalbuminemia (76.5%) (p = 0.007). Death during hospitalization was more common (14.7% vs. 0%, p < 0.001) and median length of stay was longer (14 vs. 9 days, p = 0.009) in the hypoalbuminemia group. No difference was seen in 30-day readmission (23.5% vs. 11.7%, p = 0.089). Conclusion Hypoalbuminemia was associated with a lower rate of clinical success among patients with obesity who were treated with ceftriaxone 2 grams every 12 hours. Disclosures Christina G. Rivera (O'Connor), Pharm.D, Gilead Sciences: Advisor/Consultant|Gilead Sciences: Board Member|Gilead Sciences: Grant/Research Support|Gilead Sciences: Honoraria

Abstract Background Native joint septic arthritis (NJSA) is diagnosed by synovial fluid analysis to evaluate for evidence of infection but may be definitively established by a positive gram stain or culture. Antibiotics given prior to synovial fluid sampling have been described to alter cell count, gram stain, and culture results and are conventionally deferred until after arthrocentesis to optimize diagnostic yield. However, there is limited data on the impact of preoperative antibiotic therapy on operative culture yield in the diagnosis of NJSA. Methods Following IRB approval, we reviewed medical records of adults diagnosed with NJSA who underwent surgical intervention at Mayo Clinic facilities from January 2012 to December 2021. The effect of preoperative antibiotic therapy on operative culture yield was evaluated through a paired analysis of preoperative and operative cultures results utilizing logistic regression along with generalized estimating equations (GEE) to account for correlations of multiple measurements on the same subject. Results A total of 299 patients with NJSA of 321 joints with the accompanying characteristics who underwent surgery met study criteria (Table 1). Joint distribution, microbiology, and antibiotic administration are outlined in Table 2. Among those treated with preoperative antibiotics, there was a significant decrease in yield between preoperative and operative cultures (68.0% to 57.1%, p < .0001), whereas in patients without preoperative antibiotic exposure, there was an increase in yield (60.9% to 67.4%, p = 0.244; Figure 1). Logistic regression analysis revealed that preoperative antibiotic exposure was more likely to decrease operative culture yield as compared to non-exposure (change, -10.9% vs. +6.5%; p = .006). Secondary analyses restricted to individuals who received preoperative antibiotics revealed that an increasing number of doses and earlier administration of initial antibiotic therapy were associated with lower rates of operative culture yield (Figure 2). Joint distribution, diagnostic/microbiologic, and antibiotic administration characteristics of 321 joints in 299 patients with native joint septic arthritis Composite Image 1: Figure 1, 2a/2b Figure 1: Change in Preoperative and Operative Culture Yield with Antibiotic Exposure Figure 2: Effect of Antibiotic Doses and Timing of Therapy on Predicted Probability of Operative Culture Positivity Conclusion In patients with NJSA, preoperative antibiotic exposure resulted in a significant decrease in microbiologic yield of operative cultures as compared to patients in which antibiotic therapy was held prior to obtaining operative cultures. Disclosures Brandon J. Yuan, M.D., American Association of Orthopaedic Surgeons: Board Member|DePuy, A Johnson & Johnson Company: Advisor/Consultant|Mid America Orthopaedic Association: Board Member|Stryker: Advisor/Consultant Gina A. Suh, M.D., Adaptive Phage Therapeutics: Grant/Research Support|Adaptive Phage Therapeutics: IP royalties|Phagelux: Grant/Research Support Aaron J. Tande, M.D., Musculoskeletal Infection Society: Board Member|Wolters Kluwer Health - Lippincott Williams & Wilkins: Publishing royalties, financial or material support

Abstract Background Native joint septic arthritis (NJSA) of the wrist is a rare condition, with published literature suggesting an incidence of approximately 1.5% among patients presenting with acute painful and swollen wrist. The aim of this study was to investigate the characteristics, management, and outcomes of wrist NJSA at our institution. Methods We conducted a retrospective study of all adults diagnosed with wrist NJSA who underwent surgical intervention at Mayo Clinic facilities from January 2012 to December 2021. The diagnosis was confirmed based on clinical presentation, synovial fluid white blood cell count, and aspiration or operative cultures. Results A total of 557 patients developed NJSA during the study period, of whom 55 (9.9%) were diagnosed with wrist NJSA, median age was 63, with the associated demographics (Table 1). 12 (21.8%) had a history of antecedent trauma or procedure, 11 (20%) had synchronous joint infections, and 22 (40%) had positive blood cultures. The median synovial white blood cell count was 94,050/mm3 (IQR 51,920 – 139,941 /mm3). Crystals were detected in 5 patients (8.8%). Additional diagnostic data are available in Table 2. Open debridement was performed in 35 (61.4%) patients, and the rest underwent arthroscopy. Positive Gram stain results were detected in the preoperative synovial fluid of 12 (21.8%) cases. The most common pathogen isolated was Staphylococcus aureus in 13 (24%) of cases. The median duration of antimicrobial therapy was 31 days (IQR 26 – 45 days). There was no statistically significant difference in the incidence of complications between patients who underwent open debridement and those who underwent arthroscopy (Table 3). The most common complication of both groups was compromised range of motion of the wrist joint. Conclusion Native wrist septic arthritis comprised 9.9 % of all NJSA during the study period. Concomitant bacteremia and synchronous joint infections were common, highlighting the importance of obtaining blood cultures and comprehensive joint exam in this setting. Crystals and Gram stains were detected in 10 % and 22% of cases, respectively. These findings should not rule out NJSA. Decreased range of motion was common complication, affecting 21% of all cases. Disclosures Gina A. Suh, M.D., Adaptive Phage Therapeutics: Grant/Research Support|Adaptive Phage Therapeutics: IP royalties|Phagelux: Grant/Research Support Aaron J. Tande, M.D., Musculoskeletal Infection Society: Board Member|Wolters Kluwer Health - Lippincott Williams & Wilkins: Publishing royalties, financial or material support Brandon J. Yuan, M.D., American Association of Orthopaedic Surgeons: Board Member|DePuy, A Johnson & Johnson Company: Advisor/Consultant|Mid America Orthopaedic Association: Board Member|Stryker: Advisor/Consultant

Abstract Background Achromobacter spp. are important pathogens that are most frequently implicated in opportunistic infections, especially in patients with chronic lung disease, malignancy, and solid organ or hematopoietic stem cell transplantations. They commonly cause pneumonia, bacteremia, and device-associated infections. Intrinsic and acquired resistance mechanisms usually complicate treatment. Further characterization of the changing antibiotic susceptibilities and clinical manifestations of Achromobacter spp. are needed to improve clinical practice. Methods We performed a retrospective review of Achromobacter isolates from 2013 to 2023 in the Mayo Clinic Enterprise with available antimicrobial susceptibility testing (AST) data. Variables included sample source, collection date, and AST by agar dilution with susceptibility defined according to Clinical and Laboratory Standards Institute (CLSI) breakpoints. Samples were categorized into quartiles based on collection date and grouped into source types (respiratory, genitourinary, etc.) and AST. Results A total of 1,506 patients were identified with a total of 1,546 unique Achromobacter spp. isolates from 2013 - 2023. The most common species was A. xylosoxidans, encompassing 40.1% of all isolates (Table 1). Respiratory samples (sputum, bronchoalveolar lavage) were the most common source (57.5%), followed by musculoskeletal and soft tissue (16.4%), genitourinary (12.2%), and oropharyngeal sources (10.3%). AST from 2013 to 2023 showed persistent high levels of resistance to aztreonam and tetracycline, with stable susceptibility to piperacillin-tazobactam, trimethoprim-sulfamethoxazole, and carbapenems (Table 2). Over our 10-year analysis, there was increased resistance to aminoglycosides, fluoroquinolones, ceftazidime, and cefepime.Table 1.Achromobacter Species Identification and Isolate Percentage (%) Stratified by Year Table 1 lists the Achromobacter species identified stratified by the year each sample was collected. Each value represents the number of isolates that were identified as the listed Achromobacter species, with "Achromobacter sp." indicating an isolate without species identification. Percentages of species are listed in parentheses (%). Sample totals are listed in the right column.Table 2.Antibiotic Susceptibility of All Tested Achromobacter Isolates (Percentage of Susceptible Isolates) Table 2 lists antibiotics by class, stratified by year that Achromobacter isolates were tested. Each value is the total number of isolates tested for antimicrobial susceptibility, followed by the percentage of susceptible isolates in parentheses (%). Total isolates tested and overall susceptibility percentage is also listed over the 10-year period. Conclusion Achomobacter continues to be a clinically significant organism with a complex resistance profile. Our dataset shows a significant prevalence of non-respiratory and non-genitourinary samples, in addition to increasing resistance over many antibiotic classes. Our data suggests that piperacillin-tazobactam, imipenem, and minocycline are appropriate empiric regiments for Achromobacter. Disclosures All Authors: No reported disclosures