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PURPOSE Deficient mismatch repair/microsatellite instability (dMMR, MSI-H) in biliary tract cancers (BTCs) is observed in 1%-5% of tumors. MSI-H across solid tumors has demonstrated durable response to immune checkpoint inhibitors (ICIs) regardless of the anatomic location. Here, we describe clinical outcomes and surgical conversion of MSI-H BTC treated with ICIs. Patients and Methods We conducted a multicenter, retrospective analysis of BTC patients with dMMR/MSI-H between 2017 and 2024 at Mayo Clinic, University of Michigan, and University Hospitals Seidman Cancer Center. Outcomes of interest were surgical resection rate, rate of pathologic response, 2-year overall survival (OS; time from initiation of treatment to death/last follow-up), and time to treatment discontinuation (TTD; time from initiation of treatment to cessation because of any cause). Analyses were descriptive. RESULTS Thirty patients with MSI-H BTC were identified: 19 with cholangiocarcinoma, three with gallbladder cancer, and 8 with BTC undefined. The median age at diagnosis was 61.5 years (range, 26-86). Twenty-six (86.7%) patients had advanced stage at diagnosis. Twenty-seven patients (90%) received first-line systemic therapy, and 13 (48.1%) continued onto second line. Six patients (23.1%) were restaged to resectable from advanced disease after ICI therapy and underwent resection; all remained recurrence-free at last follow-up. Of these six patients, 3 (50%) achieved a pathologic complete response. Among those receiving first-line therapy, the median TTD was 9.9 months (95% CI, 5.7 to 14.5 months) and the 2-year OS was 73% (95% CI, 56% to 94%). CONCLUSION ICI therapy in patients with MSI-H BTC demonstrated durable response and downstaged some BTC to a resectable stage. dMMR/MSI-H should be performed up-front to guide treatment decisions.

Abstract Background Unresectable hepatocellular carcinoma (uHCC) is a leading cause of cancer death. FDA-approved first-line systemic therapies include atezolizumab/bevacizumab (atezo/bev) and durvalumab/tremelimumab (durva/treme); however, there is a lack of comparative data. Methods We reviewed outcomes of patients with uHCC who initiated atezo/bev or durva/treme between 2017 and 2024, across six institutions. Overall survival (OS) and time to treatment discontinuation (TTD) were analyzed using the Kaplan–Meier and Cox models, adjusting for baseline characteristics. Results Four hundred fifty-two uHCC pts were included. Median age: 68 years; 77% male; 81% white. Most common etiologies were viral hepatitis (38.9%) and metabolic dysfunction-associated steatohepatitis (19.5%). Disease progression was the primary reason for treatment discontinuation, atezo/bev (56%) and durva/treme (42%). Outcomes were not statistically significant (median OS [month, m]: 14.0 vs 14.6 [P = .66]; median TTD [m]: 4.9 vs 3.9 [P = .42] for atezo/bev vs durva/treme). Outcomes were significantly different between Child-Pugh classes (CP: A, B7, B8/9, C) respectively, median OS(m): 19.0, 6.1, 5.1, 2.0 (P < .001); median TTD(m): 6.1, 2.3, 3.0, 1.3 (P < .001). Conclusions In this real-world study of uHCC, no significant difference in clinical outcomes was observed between atezo/bev and durva/treme in the first-line setting. CP scores were a key prognostic variable with both regimens.

PURPOSE Limited treatment options exist for patients with locally advanced or metastatic biliary tract cancers (BTCs). Recently, several clinical trials provided preliminary evidence for human epidermal growth factor receptor 2 (HER2) as a new target for patients with HER2-expressing BTC. We conducted a systematic review and pooled analysis of the safety and efficacy of anti-HER2 agents in patients with advanced BTCs. METHODS A comprehensive search of PubMed/MEDLINE and EMBASE was performed to identify phase I, II, or III clinical trials published between January 2019 and March 2024 that evaluated anti-HER2 therapy in locally advanced or metastatic BTC. Participant data included in the analysis were from trials evaluating the efficacy and safety of various anti-HER2 agents. The primary end points included objective response rate (ORR), disease control rate (DCR), and progression-free survival (PFS). The secondary end points included incidence of treatment-related adverse events (TRAEs), rate of treatment discontinuation, and death. RESULTS The analysis included 368 patients from eight publications diagnosed with advanced BTC. Patients were treated with several anti-HER2 agents including zanidatamab, pertuzumab plus trastuzumab, tucatinib plus trastuzumab, trastuzumab deruxtecan, trastuzumab plus chemotherapy, trastuzumab-pkrb plus chemotherapy, and neratinib. The pooled ORR and DCR were 34% (95% CI, 24 to 44) and 64% (95% CI, 51 to 77), respectively. The pooled weighted PFS and median overall survival were 4.8 and 9.4 months, respectively. The pooled duration of response for the reporting trials was 5.0 months. In the study cohort, 82.6% of patients experienced any adverse event and 32.1% experienced a grade 3-4 adverse event. Only 5.7% of the patients discontinued treatment secondary to TRAEs. CONCLUSION In patients with HER2-expressing BTCs, anti-HER2 therapies are viable options, particularly in the second-line setting.

639 Background: Limited treatment options exist for patients with locally advanced or metastatic biliary tract cancers (BTCs). Recently, several clinical trials provided preliminary evidence for human epidermal growth factor receptor-2 (HER2) as a new target for patients with HER2 expressing BTC. We conducted a systematic review and pooled analysis of the safety and efficacy of anti-HER2 agents in patients with advanced BTC. Methods: A comprehensive search of PubMed/MEDLINE and EMBASE was performed to identify phase 1, 2, or 3 clinical trials published between January 2019 and March 2024 that evaluated anti-HER2 therapy in locally advanced or metastatic BTC. Primary endpoints included objective response rate (ORR), disease control rate (DCR), and progression-free survival (PFS). Secondary endpoints included the incidence of treatment-related adverse events (TRAEs), rate of treatment discontinuation, and death. Forest plots were generated to summarize the results and demonstrate the effect size estimates for each study, along with their confidence intervals and the pooled estimate from the random-effects model. The random-effects models were configured to use the Restricted Maximum Likelihood method for estimating between-study variance for all analyses. Results: After excluding duplicate and irrelevant articles, data extraction and analysis were performed on eight selected clinical trials. The analysis included 368 patients with a median age of 64 (range 49-68), with 55% being female. Patients were treated with several anti-HER2 agents, including zanidatamab, pertuzumab plus trastuzumab, tucatinib plus trastuzumab, trastuzumab deruxtecan, trastuzumab plus chemotherapy, trastuzumab-pkrb plus chemotherapy and neratinib. The pooled ORR and DCR were 34% (95% CI 24-44) and 64% (95% CI 51-77) respectively. The pooled weighted PFS and median OS survival were 4.8 and 9.4 months, respectively. The pooled duration of response was 5.0 months. In our subset analysis, which included only patients who had received ≥1 prior therapy, the pooled ORR was 30% (95% CI 22-39), the pooled DCR was 62% (95% CI 48-75), and the pooled median PFS was 4.4 months. In the study cohort, 82.6% of patients experienced any adverse event, and 32.1% experienced a grade 3-4 adverse event. Only 5.7% of the patients discontinued treatment secondary to TRAEs. Conclusions: In patients with HER2 expressing BTCs, anti-HER2 therapies demonstrated preliminary signals of efficacy with manageable toxicities, particularly in the second-line setting.

532 Background: HCC accounts for 80% of primary liver cancers, and worldwide, is the third common cause of cancer-related death. Two FDA approved 1st line systemic treatment options include atezo/bev and durva ± treme. Herein we report outcomes of these regimens in the 1st line setting via a real-world, multi-institutional retrospective cohort study. Methods: We reviewed clinical outcomes of patients (pts) who initiated 1st line atezo/bev or durva ± treme for unresectable HCC between March 2017 and February 2024, across 5 institutions (Mayo Clinic, University of Alabama, Cedars-Sinai Medical Center, University Hospitals Seidman Cancer Center and University of Michigan). Time to treatment failure (TTF) and overall survival (OS) were analyzed using the Kaplan-Meier method. Best (objective) response was tabulated. Multivariable analyses were performed using Cox models and logistic regression for time-to-event and binary outcomes, respectively, while adjusting for age, sex, race, HCC etiology, Child-Pugh class, and ALBI grade. Results: A total of 433 HCC pts were included; atezo/bev (336), durva ± treme (97). Median age at the start of therapy was 68 years; 77% were male, 82% were Caucasian. Etiologies of HCC were viral hepatitis (38%), MASLD (20%), alcohol (10%), non-viral multifactorial (10%), or unknown (22%). Pts receiving durva ± treme were less likely to have cirrhosis (11% vs. 28%, p<0.01) but similar in terms of macrovascular invasion (63% vs. 58%, p=0.35) compared to pts receiving atezo/bev. Reasons for treatment discontinuation were similar between the two groups, with the most common being disease progression - atezo/bev (56%) and durva ± treme (47%). The differences in clinical outcomes were not statistically significantly and remained consistent after multivariable adjustment. (Table, atezo/bev as the reference group). Outcomes were significantly different between Child-Pugh classes (CP: A,B,C) respectively, OS: 19.0 m, 6.4 m, 1.9 m (p<0.001); TTF: 6.1 m, 2.7 m, 1.3 m (p<0.001). Conclusions: In this real-world retrospective cohort study of unresectable HCC, the differences in overall survival, objective response, and time to treatment failure were not statistically significant between atezo/bev and durva ± treme in the 1st line setting. Outcome Atezo/bev Durva±treme Univariate p-value Multivariable adjusted hazard ratio (95% CI) Multivariable adjusted odds ratio (95% CI) Overall Survival, Median (month) 14.0 14.6 0.77 0.78 (0.54-1.14) --- Time to Treatment Failure, Median (month) 4.9 4.1 0.71 0.95 (0.72-1.26) --- Objective response, % 26.3% 21.1% 0.31 --- 0.78 (0.43-1.39)

84 Background: Local therapies potentially offer a curative approach for patients with oligometastatic colorectal cancer (CRC). The effectiveness of systemic chemotherapy following definitive local treatment in this setting is not well-defined. Tumor-informed circulating tumor DNA (ctDNA) might guide management strategies after curative-intent local treatment. Methods: This is a single institution retrospective study of patients with CRC who underwent curative-intent local therapy to an isolated site of metastatic disease and had post-intervention tumor-informed ctDNA (Signatera) testing. The study was approved by the institutional review board. Clinical characteristics, including ctDNA results, were collected and evaluated. Kaplan-Meier method and log-rank test were used to calculate and compare disease-free survival (DFS). Factors associated with DFS were analyzed using multivariate Cox proportional hazards model. Results: 45 patients were included with median age of 59 years, 62% being male, 91% white, and 53% with stage IV disease at diagnosis. 37% of the patients had RAS mutations, no patient had BRAF mutation, and 2.2% patient had mismatch repair deficient disease. Isolated liver metastases were present in 80% of patients, lung metastases in 11% and other sites in 9%. 44 patients received chemotherapy prior to definitive treatment, with a median treatment duration of 16 weeks. ctDNA tests were done prior to local therapy in 23 patients, with 14 cases (61%) testing positive. Definitive treatment included resection (58%), ablation (13%), radiotherapy (4%), and multimodality (25%). Post-definitive treatment chemotherapy was administered to 24 (53%) patients. ctDNA positivity following definitive therapy was observed in 10 patients (22%), which was associated with a poorer prognosis, with a median DFS of 5.3 months compared to 21.3 months for the ctDNA-negative group (p<0.001). These findings were confirmed on multivariate analysis. In patients who had negative ctDNA after definitive local treatment, median DFS was 14.9 months for those who received post-intervention chemotherapy versus 21.3 months for those without post-intervention chemotherapy (p=0.835). Conclusions: Patients with negative ctDNA results following definitive local therapy for isolated metastatic CRC have better prognosis. Post-intervention chemotherapy in this group of patients was not associated with improved DFS. ctDNA guided omission of post-intervention chemotherapy following curative-intent local treatment of oligometastatic CRC warrants further study. [Table: see text]

50 Background: A+B is commonly used as first line systemic therapy in HCC patients with CP-B liver function, although in the IMbrave150 clinical trial, its efficacy was only assessed in patients with CP-A liver function. We evaluated outcomes in patients with CP-B liver function and compared to those with CP-A. Methods: We completed a multi-institution, retrospective review of patients with HCC from Mayo Clinic and University Hospitals Seidman Cancer Center, who had received A+B in the first line setting between March 2018 and November 2023. CP score was calculated at time of treatment, response was assessed, and progression free (PFS) and overall (OS) survival were determined using the Kaplan Meier method. Results: Among 322 patients with HCC, median age was 66.5 years, 78.6% were male, and 82.6% were white. Eighty-six patients (27%) had CP-B liver function, while 226 (70%) had CP-A and 10 (3%) had CP-C. Etiology of liver disease in patients with CP-B included hepatitis B in 7.0%, hepatitis C in 38.4%, alcohol use in 30.2%, and metabolic associated steatohepatitis in 20.9%. Median OS in patients with CP-B liver function was 6.4 months, while mOS was 21.6 months for those with CP-A ( p<0.0001). Further stratifying, mOS in those with CP-B7 was 9.1 months, CP-B8 was 5.5 months, and CP-B9 was 4.0 months. 12-month OS in patients with CP-B was 32.4%, compared to 69.3% in CP-A. Median PFS was 4.8 months in those with CP-B and 8.9 months in those with CP-A. Median PFS in those with CP-B7, -B8, and -B9 was 6.4 months, 2.7 months, and 2.7 months, respectively. Among those with CP-B, 1 patient had a complete response, 17 (19.8%) had a partial response, 29 (33.7%) had stable disease, and 37 (43.0%) had progressive disease. Adverse events in CP-B patients included hypertension in 14.0% (grade 3 in 1 patient), bleeding in 16.3% (grade 3 or greater in 11.6%), fatigue in 38.4%, and an immune-related adverse event in 17.4% (grade 3 in 5.8%). Conclusions: Patients with advanced HCC and CP-B7 liver function may still benefit from A+B. Importantly, no additional safety risks were identified in this subgroup. Those with CP-B8 and CP-B9 have significantly worse survival than those with CP-B7 and the likelihood of benefit from systemic therapy is minimal. It is important for providers to address the impact of baseline liver function on expected outcomes in patient with HCC.

Abstract Background Atezolizumab plus bevacizumab is the standard of care for advanced hepatocellular carcinoma (HCC) in the first-line setting, although was only evaluated in patients with Child-Pugh (CP) A liver function in the IMbrave150 trial. We sought to determine the outcomes of these patients based on CP score and ALBI grade in the US population. Methods This multicenter cohort study included patients with HCC who received atezolizumab with bevacizumab as first-line systemic therapy between March 2018 and November 2023. Overall survival (OS) was determined using the Kaplan-Meier method and multivariate analyses were performed using Cox proportional hazard regression method. Results Among 322 patients, 226, 86, and 10 patients had CP-A, CP-B, and CP-C liver function, respectively. Median age was 66.5 years, 78.6% were male, and 82.6% were White. Median OS (mOS) was 21.6 months for those with CP-A, 9.1 months for those with CP-B7, and 4.7 months for those with CP-B8-C12 (P &lt; .0001). Among patients with CP-A, those with ALBI grade 1 had an mOS of 34.9 months versus 14.2 months in those with grade 2. In multivariate analyses, CP score, ALBI grade, hepatitis B, performance status, and macrovascular invasion were significantly associated with survival. Conclusions CP score is an important prognostic tool for patients with HCC receiving atezolizumab plus bevacizumab, and this regimen remains a viable option for patients with CP-B7 with no additional safety concern, although the benefit is significantly less than those with CP-A. ALBI score has independent predictive value in patients with CP-A liver function.

(1) Background: Local therapies offer a potentially curative approach for patients with oligometastatic colorectal cancer (CRC). An evidence-based consensus recommendation for systemic therapy following definitive locoregional therapy is lacking. Tumor-informed circulating tumor DNA (ctDNA) might provide information to help guide management in this setting. (2) Methods: A multi-institutional retrospective study was conducted, including patients with CRC that underwent curative-intent locoregional therapy to an isolated site of metastatic disease, followed by tumor-informed ctDNA assessment. The Kaplan–Meier method and log-rank tests were used to compare disease-free survival based on ctDNA results. ctDNA test performance was compared to carcinoembryonic antigen (CEA) test results using McNemar’s test. (3) Results: Our study cohort consisted of 87 patients treated with locoregional interventions who underwent ctDNA testing. The initial ctDNA test post-intervention was positive in 28 patients and negative in 59 patients. The median follow-up time was 14.0 months. Detectable ctDNA post-intervention was significantly associated with early disease recurrence, with a median disease-free survival (DFS) of 6.63 months compared to 21.30 months in ctDNA-negative patients (p < 0.001). ctDNA detected a numerically higher proportion of recurrences than CEA (p < 0.097). Post-intervention systemic therapy was not associated with improved DFS (p = 0.745). (4) Conclusions: ctDNA results are prognostically important in oligometastatic CRC, and further prospective studies are urgently needed to define its role in guiding clinical decisions.

4099 Background: A+B is standard of care for advanced HCC in the first line setting, although was only evaluated in patients with CP class A liver function in IMbrave150. We sought to determine outcomes of patients in the real-world setting. Methods: We conducted a multi-institution retrospective analysis of patients with HCC who received A+B as first-line systemic therapy between March 2018 and November 2023, at Mayo Clinic and University Hospitals Seidman Cancer Center. Treatment response was evaluated, and progression free survival (PFS) and overall survival (OS) were determined using the Kaplan Meier method. Multivariate analyses were performed using Cox proportional hazard regression method. Results: Among patients with HCC (n=322), 226, 86, and 10 had CP-A, -B, and -C liver function, while 120, 177, and 25 had ALBI grade 1, 2, and 3 liver function. Median age was 66.5 years, 78.6% were male, and 82.6% were white. Liver disease causes included hepatitis B (5.3%) and C (34.8%), ethanol use (26.1%), and non-alcoholic steatohepatitis (15.5%). Macrovascular invasion was seen in 42.9%, and 30.4% had extrahepatic metastatic disease. Median OS for patients with CP-A5/6 was 21.6 months, B7 (n=49) was 9.1 months, and B8-C12 was 4.7 months ( p<0.0001). Median OS by ALBI grade was 34.9, 11.7, and 4.7 months for grades 1, 2, and 3. Median PFS was 8.9, 6.4, and 2.7 months for CP-A5/6, B7, and B8-C12 ( p<0.0001). Median PFS by ALBI grade was 11.0, 6.4, and 3.7 months for grades 1, 2, and 3 ( p=0.0001). Among patients with CP-A, those with ALBI grade 1 had mOS of 34.9 months versus 14.2 months for those with grade 2. Partial response was seen in 29.2%, 19.8% and 10.0% of patients with CP-A, -B, and -C, while 32.7%, 33.7%, and 40.0% had stable disease. In a univariate analysis, factors predictive of shorter OS included CP-B7 or CP-B8-C12, ALBI grade 2 or 3, hepatitis B, poorer ECOG performance status (PS), macrovascular invasion, non-white race, and lack of prior surgery or embolization. In multivariate analyses, CP score, ALBI grade, hepatitis B, ECOG PS, and macrovascular invasion were significantly associated with survival. There was significant interaction between CP and ALBI grade (Table). Conclusions: A+B remains a viable option in patients with CP-B7 liver function, although benefit is significantly less than those with CP-A. ALBI score has predictive value and can identify two prognostic groups among those with CP-A liver function. [Table: see text]