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Abstract Context Osteoanabolic therapy for osteoporosis should be followed by antiresorptive treatment (“consolidation”) to preserve bone mass. Although osteoanabolic therapy is increasingly endorsed for primary fracture prevention, real-world implementation of consolidation remains unknown. Objective To assess patterns and predictors of timely consolidation after osteoanabolic therapy for primary fracture prevention. Methods We conducted a retrospective cohort study using US commercial, Medicare Advantage, and traditional Medicare claims data. Adults aged ≥50 years who initiated romosozumab, teriparatide, or abaloparatide between 2011 and 2022 were included. The primary outcome was timely consolidation, defined as initiation of an antiresorptive medication within 3 months after osteoanabolic therapy. Secondary outcomes included delayed consolidation (initiation >3 months after completion), osteoanabolic restart following a treatment gap, and no consolidation therapy. We further distinguished participants who completed the full osteoanabolic course, defined as ≥12 months for romosozumab and ≥18 months for teriparatide or abaloparatide. Multivariable logistic regression models were used to identify predictors of consolidation patterns. Results Among 15 389 patients (mean age 70.6 years; 89% women; 85% White), 30% completed osteoanabolic therapy (median, 12.9 months for romosozumab; 23.4 months for teriparatide/abaloparatide). Overall, 25% had timely consolidation, 24% delayed consolidation, 12% restarted osteoanabolics, and 40% had no consolidation; only 12% completed therapy with timely consolidation. Timely consolidation was more likely with endocrinology (OR 1.31; 95% CI, 1.17-1.48) or rheumatology (OR 1.45; 1.30-1.62) vs primary care, and less likely among patients aged 50-64 years (OR 0.67; 0.58-0.77) vs 65-74, those enrolled in Medicare Advantage (OR 0.85; 0.74-0.98) vs traditional Medicare, or those recently hospitalized (OR 0.88; 0.80-0.97). Odds increased over time (OR 4.27; 3.63-5.05 for 2021 vs 2011 starts). Conclusion Only 1 in 4 patients received timely consolidation therapy after osteoanabolic treatment, and 1 in 8 completed the full sequence. Strategies to improve consolidation in primary fracture prevention are needed.

696 Background: EVP is the preferred 1st-line therapy for patients (pts) with aUC. Upfront EV dose reductions may be utilized to enhance tolerance and minimize treatment-related toxicities when intolerance is anticipated. Prior studies of EV monotherapy suggest that starting dose 1.25 mg/kg resulted in exposure that maximized chance of response. We hypothesize that upfront EV dose reductions would not compromise EVP efficacy. Methods: Pts with aUC treated with EVP in the multi-site UNITE database were analyzed. Upfront dose reduction was defined as starting dose < 1.25 mg/kg. Correlation between clinical features and EV dose reduction were assessed using Fisher’s Exact test. Endpoints include progression-free survival (PFS) and overall survival (OS) from EVP initiation, assessed by Kaplan-Meier analysis and Cox models. Multivariable Cox analysis (MVA) included age (< 75 vs ≥ 75), ECOG performance status (PS) (0-1 vs 2-3), hemoglobin level (< 10 vs ≥ 10), and liver metastases (present vs absent), chosen in accordance with Bellmunt criteria. Correlation with investigator-assessed observed response rate (ORR) was determined using logistic regressions. All tests were 2-sided with p < 0.05 considered significant. Results: A total of 456 pts across 17 sites were included (median age 72; 77% Caucasian; 75% male; 26% upper tract primary; 66% pure UC; 77% ECOG PS 0-1; 17% with liver metastasis; 89% 1 st line EVP). Upfront dose reduction occurred in 96 pts (21%); 76 pts (79%) started at 1.0 mg/kg and 20 pts (21%) at 0.75 mg/kg. Upfront dose reduction was significantly associated with age ≥ 75 (p = 0.002), ECOG PS 2/3 (p = 0.04), and hemoglobin < 10 (p = 0.01) but not with liver metastasis (p = 0.9). Lower starting EV dose correlated with shorter median PFS (5 vs 6 months) and OS (9 vs 10 months), and lower ORR (28% vs. 60%) when compared to full dose (Table). In MVA adjusting for prognostic factors for PFS and OS, these associations were no longer statistically significant. Conclusions: In this real-world analysis, upfront EV dose reductions were most frequently used in pts with factors associated with frailty and poor prognosis, e.g. older age and ECOG PS 2/3, and were associated with lower ORR. When adjusted for these factors, upfront EV dose reductions were not associated with shorter PFS/OS though a trend towards inferior outcomes persisted. These differences in outcomes may reflect baseline risk factors rather than dose intensity; however, prospective investigation is required to validate our hypothesis-generating results. Association of upfront EV dose reduction with outcomes. Outcome (Upfront dose reduction vs no upfront dose reduction) Univariable analysis Multivariable analysis PFS: HR (95% CI), p 1.50 (1.11 – 2.02), 0.008 1.33 (0.95-1.86), 0.09 OS: HR (95% CI), p 1.56 (1.11-2.20), 0.01 1.41 (0.96-2.06), 0.08 ORR: OR (95% CI), p 0.35 (0.21-0.60), 0.0001 0.38 (0.21-0.67), 0.0009

214 Background: 177 Lu-PSMA-617 (LuPSMA) has revolutionized care for patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC), but only half achieves PSA decline ≥50%. Biomarkers are urgently needed to improve pt selection. EVs and ctDNA released by cancer cells into the blood are emerging biomarkers to estimate overall tumor burden and capture tumor heterogeneity in mCRPC. Here, we analyzed pre-treatment plasma levels of tumor EVs and ctDNA in a pilot cohort of 35 pts with mCRPC treated with LuPSMA. Methods: Blood samples were collected pre-cycle 1 of LuPSMA at Tulane Cancer Center between 12/2018-1/2025. Plasma-derived small and large EVs were incubated with fluorescently conjugated antibodies and enumerated using nanoscale flow cytometry. ctDNA fraction was estimated from plasma cfDNA methylation WGS (∼10×) with ichorCNA. We also analyzed EVs from blood samples of male healthy donors (HD) and pts with localized prostate cancer (LPC) collected 1 day to 8 months after radical prostatectomy (post-RP) from 6/2020-8/2024 at Mayo Clinic as controls. Results: Median age at collection for 10 HD was 55 yrs and for 36 pts with LPC post-RP was 65 yrs. Median PSMA+ EV level was 2.0 x 10 6 /mL for post-RP and 1.4 x 10 6 /mL for HD. For 35 pts with mCRPC, 25 pts had complete data for analysis. Median PSMA+ EV level was 1.4 x 10 7 /mL, significantly higher than post-RP (p<0.001) and HD (p<0.001). At LuPSMA start, median age was 69 yrs (range 54-83), PSA was 82 ng/mL (range 0.8-503), median time from CRPC diagnosis to start was 50 months (range 6.9-285), median time from plasma collection to treatment initiation was 0.5 months (range 0-7.3). Median number of prior lines of life-extending therapy was 4 (range 1-11), including 100% androgen receptor pathway inhibitor and 75% docetaxel. Pts received median 4 cycles of LuPSMA. Median ctDNA fraction was 14.0% (range 0-51.1). Median time to reach nadir PSA for pts with any decline was 2.6 months. 15 pts (60%) achieved PSA40 (defined ≥40% decline in PSA from start to nadir) (range -99% to -42%) compared to 10 pts (40%) who did not (range -16% to rise), which predicted better median overall survival (OS) after LuPSMA start (40.7 v 6.0 months; HR 0.23, 95% CI, 0.07-0.71; p=0.0001). Pts were classified as LuPSMA responders using PSA40. Responders had a lower ratio of large to small PSMA+ EVs (0.30 v 0.53, p=0.0042) with an area under the receiver operating characteristic curve (AUC) of 0.83 (95% CI, 0.68-0.99), and a lower median ctDNA fraction (6.1% v 26.2%, p=0.0044) with an AUC of 0.83 (95% CI, 0.68-1.00). Incorporating both PSMA+ EV and ctDNA fraction together predicted PSA40 response with an AUC of 0.93 (95% CI, 0.84-1.00, p=0.0003). Conclusions: Using pre-LuPSMA plasma samples from a heavily pre-treated historical cohort, we integrated non-invasive liquid biopsy methods to successfully predict response to LuPSMA using PSA decline. Prospective validation is underway.

INTRODUCTION: Despite the widespread use of ursodeoxycholic acid (UDCA) in primary biliary cholangitis (PBC), many patients remain at risk of progression. Emerging data suggest that normalization of alkaline phosphatase (ALP) and total bilirubin (TB)—particularly when TB < 0.6 times the upper limit of normal (× ULN)—is associated with improved outcomes compared with ALP reduction to < 1.5 × ULN. This study investigated the association between ALP normalization in response to UDCA and long-term clinical outcomes in a real-world cohort of patients with PBC. METHODS: We compared complication-free survival in patients achieving an ALP > ULN and < 1.5 × ULN (adequate response) with those with an ALP ≤ ULN on UDCA monotherapy. Complication-free survival was defined as the absence of serious liver-related clinical events. Restricted mean survival time was used to quantify survival time gained. RESULTS: Patients achieving normal ALP and/or TB ≤ 0.6 × ULN demonstrated significantly improved complication-free survival compared with those with an adequate ALP response. Event-free survival was extended by 1.34 years (95% CI: 0.56, 2.11; P = 0.001) for ALP normalization alone, 3.7 years (95% CI: 3.11, 4.29; P < 0.001) for TB ≤ 0.6 × ULN, and 4.51 years (95% CI: 4.13, 4.88; P < 0.001) for those meeting both criteria. The risk of severe clinical events was reduced in patients achieving ALP normalization (hazard ratio [HR] 0.34; 95% CI: 0.15, 0.80; P = 0.01), TB ≤ 0.6 × ULN (HR 0.23; 95% CI: 0.09, 0.55; P = 0.001), or both (HR 0.14; 95% CI: 0.05, 0.38; P < 0.001). High-risk patients, defined by liver stiffness measurement ≥ 10 kPa or clinical, histological, or laboratory evidence of cirrhosis or portal hypertension, derived the greatest benefit. DISCUSSION: Achieving normal ALP and TB ≤ 0.6 × ULN is associated with significantly improved complication-free survival, particularly in high-risk patients. These findings highlight the potential of biochemical thresholds as a meaningful therapeutic goal in PBC management.