Sonbol, Bassam Bassam

Abstract BACKGROUND Von Hippel-Lindau (VHL) disease is a hereditary cancer syndrome characterized by development of multiple neoplasms, including central nervous system (CNS) hemangioblastomas, renal cell carcinoma (RCC), pancreatic neuroendocrine tumors (pNETs), and retinal hemangioblastomas. Belzutifan, a hypoxia-inducible factor 2-alpha (HIF-2α) inhibitor, has demonstrated efficacy in treating VHL-associated tumors. This study evaluates our institutional experience with belzutifan in patients with VHL-related tumors. MATERIAL AND METHODS We conducted a retrospective cohort study across three Mayo Clinic sites, including patients aged ≥18 years with genetically confirmed VHL disease who received belzutifan between October 2021 and March 2025. Clinical/radiological data, and adverse events (AEs) were extracted from electronic health records. Tumor responses were assessed using RECIST v1.1 criteria for RCC, pNET, CNS hemangioblastoma. Retinal hemangioblastoma responses were evaluated through ophthalmologic assessments. RESULTS Forty-five patients were included (median age 44 58% female). Sixty-seven percent had RCC, 91% had CNS hemangioblastomas, 53% had pNETs, and 62% had retinal hemangioblastomas. The median duration of belzutifan therapy was 22.6 months (range 1.0-41.4 months). Among patients with RCC (n=26), overall response rate (ORR) was 19% and median time to best response (MTBR) was 7.4 months. Five patients had partial response (PR), 15 had stable disease (SD), and 1 had progressive disease (PD). For CNS hemangioblastomas (n=41), ORR was 12%, MTBR was 6.2 months. 5 patients had PR, 30 had SD, and none had PD. For pNET (n=17), ORR was 41%, MTBR was 8.2 months. One patient had CR, 6 patients had PR, 6 had SD, none had PD. For retinal hemangioblastomas (n=28), 6 (21%) showed improvement, 9 (32%) remained stable, and 3 (11%) showed progression. MTBR was 6.7 months. Treatment-related AEs occurred in 98% of patients. Common AEs included anemia (89%), fatigue (80%), hypoxia (18%), and headache (13%). Grade 3 AEs were observed in 20% of patients, including anemia (7%), hypoxia (9%), fatigue (4%), pneumonitis (2%), loss of consciousness (2%). One patient experienced a grade 4 event (status epilepticus). Anemia management involved iron supplementation (n=11), RBC transfusion (n=3), dose reduction (n=2), treatment holiday (n=8), permanent discontinuation (n=1). Hypoxia management included dose reduction (n=1), treatment holiday (n=3), discontinuation (n=1). CONCLUSION Belzutifan shows clinical activity across various VHL-associated neoplasms in real-world practice, with a manageable safety profile. The lower ORR compared to the phase III trial may reflect differences in baseline disease, including lower tumor burden in our cohort. These findings support its continued use in VHL disease, with attention to monitoring and managing treatment-related AEs.

Abstract Background Cardiac metastasis from neuroendocrine tumors (NET) is rare and has been thought to potentially result in life threatening sequalae. Peptide receptor radionucleotide therapy (PRRT), such as Lutetium-177 (Lu-177) DOTATATE, has been validated as effective treatment for patients with NET who have progressed on somatostatin analogue (SSA) therapy and more recently suggested for use in SAA-naïve higher risk grade 2 and grade 3 NETs. However, Lu-177 DOTATATE therapy has been found to have potentially serious adverse effects both locally and systemically. Overall, the clinical significance of cardiac metastasis of NET, as well as the safety and efficacy of Lu-177 DOTATATE in this cohort, has not been thoroughly evaluated. Purpose This study assessed the outcomes and clinical consequences of cardiac metastatic involvement in patients with NET. Furthermore, this study investigated the safety of Lu-177 DOTATATE therapy in patients with cardiac metastases from NET. Methods All patients who underwent 68Ga-DOTATATE positron emission tomography for evaluation of NET across three tertiary centers between 2016 and 2022 were retrospectively evaluated. Patients with evidence of cardiac metastasis were further evaluated. Baseline characteristics, treatment modality, and clinical outcomes including mortality, arrhythmia or conduction disease, carcinoid heart disease, and heart failure admissions were recorded. Patients with cardiac metastases were grouped and compared based on therapeutic modality (conservative therapy with surveillance or SSA, Lu-177 DOTATATE therapy, or surgical resection of metastases). Results From 3253 patients with NET, 51 patients were identified to have cardiac metastases (mean age 66.7 ± 12.2 years, 54% male). Three patients underwent surgical resection of cardiac metastases, and in two of whom this was concomitant while undergoing valve surgery for carcinoid heart disease. Patients with cardiac metastasis had significantly higher mortality than patients without cardiac metastasis (HR 2.12, 95%CI 1.00 – 4.52, p = 0.049, Figure 1A). Median follow-up from diagnosis of cardiac metastasis was 3.64 years [IQR 1.59 – 5.64]. There was no significant difference in clinical outcomes between patients that received Lu-177 DOTATATE therapy (n = 27) and conservative therapy (n = 21). Specifically, there was no significant difference in mortality risk at five years post the diagnosis of cardiac metastasis between these groups (p = 0.47, Figure 1B). Conclusion Patients with cardiac metastasis from NETs have worse clinical outcomes than NET patients without cardiac metastatic involvement. Lu-177 DOTATATE therapy appears to be safe in patients with cardiac metastasis from NET.Figure 1AFigure 1B

688 Background: PACC is a rare malignancy originating from the exocrine pancreas, accounting for less than 1% of all pancreatic cancers. Due to the rarity of the disease entity, there is a paucity of data to guide treatment decisions. This retrospective study aims to provide additional clinical characteristics and outcomes to aid in future treatment decisions. Methods: Pathology records from Mayo Clinic (AZ, FL, MN) patients (pts) denoting acinar or mixed-acinar cell carcinoma were searched between 2002 to 2023 and selected for retrospective review. Pt demographics, treatment courses, and next generation sequencing (NGS) were collected. Results: A total of 62 pts (74% male, n = 46) were identified with median age 64 years old. Histologic subtypes were 67% pure acinar cell carcinoma (42/62), 24% mixed acinar-neuroendocrine (15/62), and 8% mixed acinar-adenocarcinoma (5/62). AJCC stages at diagnosis were 34% stage I/II (21/62), 16% stage III (10/62), and 50% stage IV (31/62). Early-stage disease was treated with upfront surgical resection (81%, 17/21). Locally advanced disease received neoadjuvant therapy (NAT) followed by surgical resection (80%, 8/10). FOLFIRINOX was most often chosen as NAT (65%, 11/17), while others received gemcitabine-based NAT. The R0 resection rate was 86%. The 3 and 5-year survival estimates for stage III were 90.9% (95% CI: 75.4 – 100%) and 67.3% (95% CI: 42.3 – 100%), respectively. The 3 and 5-year survival estimates for stage IV were 36.6% (95% CI: 18.6 – 71.9%) and 29.3% (95% CI: 13.1 – 65.5%), respectively. Median survival time for stage IV was 3 years. Somatic NGS testing was done in 24 pts with alterations found in: homologous recombination (HR) in 42% (10/24); RAF alterations in 25% (6/24); mismatch repair (MMR) in 13% (3/24; none of them with MMR germline mutations), 1 ETV6-NTRK3 fusion, and 1 FGFR mutation. Germline NGS testing was done in 21 pts and alterations in HR were seen in 33% (7/21) of pts. This led to additional therapeutic options in 46% (11/24) of pts. Conclusions: Unlike PDAC, PACC is a genomically diverse disease, with potentially targetable alterations in RAF, HRD, and MMR genes, offering additional therapeutic options for significant number of pts. In addition, more than one-third of the pts harbored germline mutations in HR genes. Therefore, somatic and germline testing should be considered for any pt diagnosed with PACC.

592 Background: The introduction of peptide receptor radionuclide therapy (PRRT) using Lutetium-177 (177Lu) DOTATATE has led to a paradigm shift in the treatment of neuroendocrine tumors (NETs). Hematological toxicity is a well-recognized adverse effect (AE) of 177Lu DOTATATE. Most cytopenias are transient, with an estimated incidence of 10-25%, typically mild to moderate in severity (grade G1-2). The most dreaded AE of PRRT is therapy-related myeloid neoplasm (t-MN), with an estimated 2-8% incidence and a higher incidence reported in patients who also received prior chemotherapy. We sought to evaluate the hematological safety of 177Lu PRRT in the setting of NETs with extensive (i.e., innumerable) bone metastases. Methods: We retrospectively reviewed the medical records of all Mayo Clinic patients (pts) with extensive/innumerable osseous metastases, defined as >50% skeletal involvement by positron emission tomography (PET) DOTATATE, who were treated with 177Lu DOTATATE. Pts characteristics and laboratory results were collected before, during, and after 177Lu DOTATATE treatment. Hematotoxicity was graded according to the NCI-CTCAE v5. Results: Out of 27 pts, 13(48%) developed cytopenia(s) of any grade after treatment with one or more cycles of 177Lu DOTATATE. In total, there were 13(48%) pts with anemia, 13(48%) with thrombocytopenia, and 6(22%) with neutropenia. Six (22%) pts had severe hematological toxicity (G3-4). Twelve months post-PRRT, 7(26%) pts continued to experience cytopenia(s) of any grade, of whom 4(15%) had G3-4 hematotoxicity. One pt developed t-MN, and two pts had myelophthisis on bone marrow biopsy from infiltrating NET. 16(59%) pts received cytotoxic chemotherapy before PRRT, and 7(25.9%) developed subsequent cytopenia(s). Overall, 15(55%) pts completed four cycles, while 3 pts didn’t complete four cycles of 177Lu DOTATATE due to hematotoxicity. Conclusions: Pts with advanced NETs and extensive/innumerable bone metastases treated with PRRT could be at higher risk for myelosuppression than historical controls. Our study highlights the importance of carefully monitoring and assessing hematological parameters in pts being considered for 177Lu DOTATATE with extensive/innumerable bone metastasis. [Table: see text]

55 Background: Nearly one-half of deficient mismatch repair (d-MMR) metastatic colorectal cancers (mCRC) demonstrate durable responses to immune checkpoint inhibitors (ICIs). Given preclinical data indicating that liver metastases sequester activated CD8+ T cells from systemic circulation, we examined clinical outcome by metastatic site. Methods: In a retrospective cohort of patients with d-MMR mCRCs treated at multiple centers in France (n=66), we sought to validate data from a U.S. cohort, and then performed pooled analysis (n=104). All patients received first-line ICI monotherapy. Metastatic site was analyzed in relationship to tumor response (RECIST version 1.1), and progression-free survival (PFS) by multivariable stratified Cox regression after adjustment for covariates. Results: Objective responses were achieved in 38/66 (58%) patients in the validation cohort. Best tumor response included 13 (20%) complete responses (CR), 25 (38%) partial responses (PR), 16 (25%) stable disease, and 11 (17%) progressive disease (PD). One-year and 5-year PFS rates were 73% and 67%, respectively; 18 (27%) patients progressed during immunotherapy. Best tumor response was attenuated in patients with liver metastasis ( P=0.03). Presence of liver metastasis, but not other sites, was associated with significantly poorer PFS after adjustment for covariates (HRadj 2.82; 95%CI, 1.08-7.39; Padj=0.03). In a pooled analysis, liver metastasis remained significantly and independently associated with poorer PFS (HRadj 3.18; 95%CI, 1.52-6.67; Padj=0.002) and with attenuated tumor best response (P=0.01). Conclusions: Metastasis to the liver, but not other sites, was validated as an independent factor associated with poorer response and survival after ICI treatment in d-MMR mCRCs. These data underscore the need for novel therapeutic strategies in these patients. [Table: see text]

200 Background: We developed and validated a quantitative segmentation algorithm (QuantCRC) to predict disease recurrence in stage I-III colorectal cancer patients (pts) based on the analysis of digitized hematoxylin and eosin (H+E) stained pathology slides. In this study, we aim to determine if QuantCRC analysis on pre-treated RC biopsies can predict pathological complete response (pCR) after NAT which include total neoadjuvant therapy (TNT), chemoradiation (CRT) and others. Methods: Stage II-IV RC pts treated with curative intent modalities between 2005-2023 at Mayo Clinic and University of Pittsburgh were evaluated. Eligible pts had pre and post-treatment tissue available for analysis. Clinical characteristics, treatment, and outcome data were extracted from the medical record. QuantCRC extracted 15 features: %tumor, %stroma, tumor:stroma ratio, %TB/PDC, %mucin, %necrosis, %high-grade, %signet ring cells, tumor-infiltrating lymphocytes (TILs) per cm2 of a tumor, %immature stroma (tumor bed), %inflammatory stroma (tumor bed), %mature stroma (tumor bed), %immature (stromal region), %inflammatory (stromal region), and %mature (stromal region). The associations between the QuantCRC features and pCR were evaluated using Wilcoxon rank-sum tests and logistic regression models while adjusting for primary tumor location and NAT. Results: The identified 288 pts had the following demographics: median age 60, 59% male, 52% distal tumor, 42% TNT. Pts who achieved pCR had smaller pre-treatment tumors (p=0.03), higher TILS, and lower %immature (stroma) (Table 1). After multivariable adjustment, higher TILS and lower %immature (stroma) remain to be significantly associated with a higher likelihood of pCR. A higher %mature (stroma) and %mature stroma (tumor bed) were also identified, in multivariable models, to be associated with a higher rate of pCR. NAT protocol and tumor location (proximal vs. distal) were not associated with pCR. Conclusions: The ability to integrate pathological features with AI may allow for personalized treatment. Using this technology, we recognize that patients who harbor a more mature stromal archetype and inflammatory tumor predisposition, are more likely to achieve pCR to conventional NAT. These pathological features are not currently incorporated into risk stratification in RC. Additional validation and integration into current risk stratification methods is warranted. [Table: see text]

175 Background: Alterations to mismatch repair (MMR) genes such as MLH1, MSH2, MSH6, and PMS2, can lead to microsatellite instability-high (MSI-H) tumors. MMR mutations can be inherited in Lynch syndrome (LS) but can also be a result of de novo alterations resulting in MSI-H malignancies. Treatment with immune checkpoint inhibitors (ICIs) have been shown to improve survival in such patients (pts) compared to systemic chemotherapy. However, there is a paucity of information in the literature with respect to outcomes of pts with germline vs somatic MMR mutations in MSI-H colorectal cancer (CRC). Furthermore, the presence of underlying BRAF mutation confers resistance to chemotherapy in pts with CRC, however data regarding outcomes with immunotherapy in such pts with MSI-H CRC is lacking. Methods: Pt records from the Mayo Clinic (AZ, MN, FL) between 2008-2023 denoted as MSI-H CRC, were included for retrospective review. Pt demographics, treatment courses, and genomic profiles were collected. Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method. Outcome differences between sub-groups were accessed with the log rank test and univariate analyses were assessed with Cox-regression. Results: A total of 81 pt records were identified (n = 18 LS, n = 63 non-LS). Stage IV disease was found in 28% of LS pts vs 59% of non-LS pts at diagnosis. Pembrolizumab was the most common ICI selected for metastatic CRC pts for both LS and non-LS pts (65% vs 94%) with median treatment duration for each group 11.7 vs 8.8 months. There were no differences in OS or PFS for any stage between LS vs non-LS. Median OS for all patients was 82 months. For all stage IV patients, median OS was 44 months, and median PFS was 19 months. Interestingly, for stage IV pts treated with immunotherapy, tumors that harbored BRAF V600E mutation (n = 21) vs BRAF wild type (n = 20) had a significantly lower median OS 19 vs 113 months (HR = 2.69, p = 0.043) as well as median PFS 12 vs 95 months (HR = 2.48, p = 0.041). Conclusions: In this study, we found that patient treated with ICIs have similar outcomes in the presence of germline vs. somatic MMR mutations in MSI-H CRC. The presence of an associated BRAF V600E mutation, which occurs in non-LS MSI-H CRC conferred worse outcomes.

162 Background: There is a need to improve current risk stratification of stage II and III colorectal cancer (CRC) to better inform risk of recurrence and guide adjuvant chemotherapy. The purpose of this study is to examine whether integration of QuantCRC, an AI-based digital pathology biomarker utilizing hematoxylin and eosin-stained slides, provides improved risk stratification over current American Society of Clinical Oncology (ASCO) guidelines. Methods: ASCO and QuantCRC-integrated risk schemes were applied to an observational cohort of 1,068 stage II and III CRCs. The stage II integrated scheme utilizes pT3 vs. pT4 and QuantCRC-derived risk groups. The stage III integrated scheme utilizes pT1-3 vs. pT4, pN1 vs. pN2, and QuantCRC-derived risk groups. Performance metrics included log-rank test, hazard ratios and Somers’ Dxy rank correlation. Results: Integration of QuantCRC provides improved risk stratification compared to the ASCO scheme for stage II and III CRC. The QuantCRC-integrated scheme placed more stage II tumors in the low-risk group compared to the ASCO scheme (69.3% vs. 60.4%) without decreased 3-year RFS. The QuantCRC-integrated scheme provided larger hazard ratios (HR) for both intermediate-risk (3.04, 95%CI 1.81-5.10, P=2.8x10-5) and high-risk (4.62, 95%CI 2.02-10.61, P=0.0003) groups compared to ASCO intermediate-risk (2.09, 95%CI 1.21-3.63, P=0.008) and high-risk (3.08, 95%CI 1.57-6.01, P=0.001) groups. The QuantCRC-integrated scheme for stage III tumors identified a small group of 80/518 (15.4%) CRCs at very high risk of recurrence with HR of 4.08 (95%CI 2.68-6.23, P=6.5x10-11) compared to a HR of 2.42 (95%CI 1.72-3.38, P=3.1x10-7) for 228/518 (44.0%) high-risk CRCs in the ASCO scheme. QuantCRC-integrated risk groups remained prognostic in stage III CRCs when stratified by presence or absence of any adjuvant chemotherapy. No difference in RFS were seen in QuantCRC-integrated low-risk and intermediate-risk stage III CRCs stratified by 3 vs. 6-months of oxaliplatin-based adjuvant chemotherapy suggesting that these two groups can be treated with 3-months of adjuvant therapy. Conclusions: Incorporation of QuantCRC into risk stratification provides a powerful predictor of RFS that has potential to guide subsequent treatment and surveillance.

4027 Background: DKN-01 is an anti-DKK1 mAb which has demonstrated anti-tumor activity in patients with advanced GEA with low tumor PD-L1 expression, a subset with very limited therapeutic options. DKN-01 has immunomodulatory activity, stimulates a pro-inflammatory tumor microenvironment, and upregulates PD-L1 levels. Here we present 2-year survival data for 1L advanced GEA patients who received combination treatment with DKN-01, the Fc-optimized anti-PD-1 tislelizumab, and CAPOX chemotherapy. The ORR was previously reported (68% in ITT and 79% in PD-L1-low populations). Methods: This Phase 2, multi-center, single arm Part A of the DisTinGuish (NCT04363801) study investigated DKN-01 + tislelizumab + CAPOX as 1L therapy in advanced HER2(-) GEA, regardless of DKK1 and PD-L1 expression levels. Tumor DKK1 and PD-L1 were assessed by central laboratories. The primary endpoint was ORR in a modified intent to treat population (>1 dose DKN-01); secondary endpoints included PFS and OS in the ITT population. Results: Twenty-five patients were enrolled from September 2020 to April 2021. As of 23 January 2023: Median age was 61 years (22, 80); 17 patients had GEJ adenocarcinoma; 8 had gastric cancer. Twenty-one patients had tumors with evaluable DKK1 expression. Twenty-two patients had tumors with evaluable PD-L1 expression; the majority (73%) were low expressors (vCPS <5%). Median (m) duration on treatment is 11.3 months (mo). Seven patients remain on study, with 4 on-treatment beyond 2 years. The mPFS is 11.3 mo in the overall ITT population and 10.7 mo in patients with low tumor PD-L1 expression. The mOS is 19.5 mo in the overall ITT population and 18.7 mo in the patients with low tumor PD-L1 expression. Treatment related adverse events (TRAEs) were mild with most G1/2. The most common AEs related to the study drug regimen were nausea (72%), diarrhea (64%) and fatigue (60%). Five patients experienced G3 DKN-01-TRAEs including decreased neutrophil count (1), diarrhea (1), vomiting (1), hypophosphatemia (2), and pulmonary embolism (1). Conclusions: At 2-years of follow-up, 1L treatment of advanced GEA patients with DKN-01 in combination with tislelizumab and CAPOX resulted in a prolongation of PFS and OS compared with the modern SOC regimen of nivolumab plus chemotherapy, both in the overall population (mPFS 11.3 vs 7.7 mo; mOS 19.5 vs 13.8 mo) and in the PD-L1 low subgroup (mPFS 10.7 vs 7.5 mo; mOS 18.7 vs 12.4 mo), alongside a manageable safety profile. The prolonged PFS and OS observed in the current study are notable, especially in our trial population dominated by patients with tumors of low PD-L1 expression, where the known benefit of anti-PD-1 therapy is limited. The ongoing Part C of this study is evaluating mFOLFOX6/CAPOX plus tislelizumab with or without DKN-01 in the same 1L GEA patient population. Further evaluation of biomarkers is also ongoing. Clinical trial information: NCT04363801 .

57 Background: Metastatic colorectal cancer (mCRC) with deficient DNA mismatch repair (dMMR) or microsatellite instability-high (MSI-H) show frequent and durable responses to programmed cell death -1 (PD-1) blockade. While the majority of these tumors are sporadics and observed in elderly patients, first-line data are limited to the KEYNOTE-177 study. Here, we report a consecutive series of elderly patients with dMMR mCRC treated with pembrolizumab in routine clinical practice that includes analysis of clinical outcome based on metastatic site. Methods: Patients with dMMR mCRC received first-line pembrolizumab (200 mg every 3 weeks) (N = 41) at Mayo Clinic and Mayo Clinic Health System (2015-2022). Clinicopathological features including metastatic site and molecular data ( BRAFV600E, KRAS) were analyzed in relationship to tumor response rate (RECIST version 1.1). Furthermore, these variables were also analyzed in relationship to patient progression-free survival (PFS) using Kaplan-Meier methodology and multivariable stepwise Cox regression. Results: Among patients with dMMR mCRC, 29/41 (70.7%) were female, 30 (78.9%) harbored BRAFV600E, and 32 (80%) were sporadic. Median age at start of treatment was 80.6 years (IQR of 75.9, 85.9) and median number of treatment cycles was 9 (IQR: 4, 20). At a median follow-up of 23 months (range, 3.0 to 88.5), patient median PFS was 21.3 months (95% CI: 6.4, 38.5). An overall response was observed in 48.8% (20 of 41) of patients including 13 (31.7%) complete (CR) and 7 (17.1%) partial responses (PR). The median duration of response was 42.2 months (95%CI: 8.6, NR). Patients with metastases that included liver had significantly poorer PFS compared to those with non-liver metastases (HRadj 3.40 (95%CI: 1.27-9.13); Padj= 0. 01). In this regard, responses (CR, PR) to pembrolizumab were observed in 3 (21.4%) patients with liver metastasis compared to 17 (62.9%) of those with non-liver metastases. Treatment-related grade 3 or 4 adverse events were observed in 9 (22.0%) patients of whom two discontinued therapy, and there was one treatment-related death. Conclusions: First-line therapy with pembrolizumab for dMMR mCRC significantly prolonged survival in an elderly patient population with manageable toxicity in routine clinical practice. Moreover, the survival benefit of pembrolizumab was significantly attenuated in patients with liver vs non-liver metastases.