Mahadevia, Himil

Introduction: NGS is increasingly being utilized to identify pathogenic somatic and targetable variants in patients with newly diagnosed AML and MDS. Patients with high-risk disease are typically recommended to undergo allo-HCT as consolidation, upon achieving morphological complete remission (CR). But, despite achieving hematologic CR, patients often have detectable somatic variants pre allo-HCT that predict for increased risk of disease relapse. Longitudinal monitoring of somatic variants via NGS at diagnosis, pre-allo-HCT and post allo-HCT can assist in prognostication and identify patients that remain at high risk of relapse despite allo-HCT. Methods: Patients with AML or MDS who underwent a first allo-HCT and completed NGS testing at day +100 between years 2016 to 2021 were identified from the transplant registry of Mayo Clinic in Florida. The primary aim of the study was to evaluate the prognostic impact of detectable variants via NGS at day +100 days post allo-HCT on the following outcomes: 1) overall survival (OS), 2) relapse, 3) progression-free survival (PFS), and 4) non-relapse mortality (NRM). Disease risk was assessed based on European Leukemia Network (ELN) 2022 risk classification for AML and Revised International Prognostic Scoring System (R-IPPS) for MDS. Baseline variables were compared between patients with and without mutation at day +100 days post allo-HCT using Wilcoxon rank sum test for continuous variables and Fisher's exact test for categorical variables. Kaplan-Meier (KM) method was used to estimate freedom from events at different time points and draw corresponding survival curves. Results: 105 patients who underwent allo-HCT for AML and MDS and completed NGS testing at day +100 were included in the study population. Median age of the study population was 63 years (22-74) and 58% were of the male gender. Median HCT comorbidity score (HCT-CI) and KPS Karnofsky performance score (KPS) were 3 (0-8) and 90 (60-100), respectively. Matched unrelated donor (50%) and peripheral blood stem cells (98%) were the most common donor and graft source, respectively. Median number of lines of therapy pre allo-HCT was 1(0-6) and 52 (50%) patients had detectable variants after completion of chemotherapy and prior to allo-HCT. Seventeen (16%) had detectable variants via NGS on day +100. Eleven (65%) of these 17 had variants pre-allo-HCT and amongst the 88 patients with no variants post allo-HCT, 41 (47%) had detectable variants pre allo-HCT. There was no significant difference in baseline characteristics between patients with detectable variants at day+100 versus those who did not except for a higher KPS in patients with no variants at Day +100 of 90 (60-100) vs. 80 (60-100) (p=0.003). At a median follow up of 1.4 years (0.1-5.5), presence of a variant at day +100 was associated with inferior 4-year OS (32% vs. 69%, p<0.001) and higher relapse risk (64% vs. 23%, p<0.001). In univariate models, a lower KPS and presence of variants post allo-HCT were significantly associated with inferior OS, high relapse risk and worse PFS. Presence of variants pre allo-HCT was associated with an inferior PFS but did not impact OS or relapse risk. In multivariate models, KPS remained significant for OS, PFS and NRM; presence of variants at day +100 post allo-HCT approached significance for OS (p=0.06) and PFS (p=0.08) and was significant for relapse risk (p=0.002) (Table1) (Figure 1). Data regarding longitudinal evolution of variants and impact of individual variants on long term outcomes will be included at the time of presentation. Conclusion: These results indicate that presence of detectable somatic variants at day +100 is associated with poor long-term outcomes and predicts for high risk of disease relapse. Longitudinal monitoring of somatic variants via NGS should be consistently incorporated in the management of patients with high-risk AML and MDS undergoing allo-HCT. Patients with detectable somatic variants post allo-HCT should be considered for additional intervention to mitigate relapse risk.

e20535 Background: Malignant peritoneal mesothelioma (MPM) is a rare disease with about 600 new cases per million people diagnosed annually in the U.S. High incidence of germline mutations has been reported in MPM patients (pts) without asbestos exposure. However, the incidence rate of developing multiple primary cancers in this population is unknown. The aim of this study is to investigate the frequency of additional malignancies in MPM pts. Methods: Using the Mayo Clinic Cancer Registry, we identified 64 pts who were treated for MPM from January 2002-December 2022 with updated follow-up data until 01/15/2023. Electronic medical records were reviewed. Results: Among the patient cohort, 25 pts were male, and 39 pts were female. 14/64 (22%) pts were found to have at least one additional malignancy, including breast cancer (4/14, 29%), colon cancer (3/14, 21%), lymphoma (3/14, 21%), ovarian cancer (2/14, 14%), melanoma (2/14, 14%), anal squamous cell carcinoma (1/14, 7%), papillary thyroid cancer (1/14, 7%), Chronic lymphocytic leukemia (1/14, 7%), renal cell carcinoma (1/14, 7%), squamous cell carcinoma of tongue (1/14, 7%), hepatocellular carcinoma (1/14, 7%) and pituitary macroadenoma (1/14, 7%). 4/14 (29%) pts had more than one (2-4) non-MPM malignancies. The median age at diagnosis of MPM was 65 years (44-82). The median age at diagnosis of non-MPM malignancies was 66 years (18-81). Most of the patients (11/14) were diagnosed with non-MPM malignancy within 12 months of diagnosis of MPM. Most pts (11/14, 78%) were diagnosed with non-MPM malignancy first, among which 5 pts (45%) were found to have MPM on surveillance scans. Germline mutation information was not available except for 2 pts with known family history (FH) of Lynch syndrome and Li-Fraumeni syndrome. FH was available in 29 pts, out of which 28 pts had FH of cancer identified in first-degree relatives. Among the 14 pts with additional malignancies, 9 pts had FH of cancer in first-degree relatives. Among all pts, 15 (18%) pts had a history of asbestos exposure. Among pts who also had non-MPM malignancies, 3/14 (21%) pts had a history of asbestos exposure. Among the 21 non-MPM cancers, 1/21 (5%), 11/21(52%), 1/21(5%), 3/21(14%), and 5/21(24%) non-MPM malignancies were stage 0, stage I, II, and III, or unknown at the diagnosis respectively. All except 1 pt underwent curative treatment for their non-MPM malignancies, and 12 pts had no evidence of disease at death or the time of last follow-up. Conclusions: The rate of multiple primary malignancies in pts with MPM is high, indicating possible genetic predisposition associated with this disease. Early genetic consultation and evaluation for germline mutations may need to be considered for these pts to improve long-term outcomes.

e18097 Background: Sorafenib and lenvatinib are FDA-approved MKIs for locally recurrent or metastatic, progressive, DTC refractory to radioactive iodine treatment. Cabozantinib showed a survival benefit in radioiodine-refractory DTC previously treated with sorafenib and/or lenvatinib and was granted FDA approval. Our study aims to investigate the benefit of other MKIs in DTC beyond the first-line setting. Methods: DTC patients (pts) treated with multiple lines of MKIs from August 2018 to July 2022 at Mayo Clinic across all sites were identified. Electronic medical records were reviewed. 6-month, 12-month, and 18-month progression-free survival (PFS) were calculated for all lines of therapy using RECIST 1.1 criteria. Results: Among the 9 pts identified, 4 were male. The median age was 65 years (43-75). Most pts (60%) had papillary thyroid cancer. All pts received lenvatinib as first line treatment. The 6, 12 and 18-month PFS were 89%, 89%, and 55% respectively. 6 pts discontinued lenvatinib due to progression of disease (PD). 3 pts discontinued it due to adverse effects (AEs), which included hemoptysis (1 pt), severe rash (1 pt) and multiple psychiatric manifestations (1 pt). 8 pts received pazopanib, and 1 patient received cabozantinib with ipilimumab (1 dose) and nivolumab (6 months - discontinued due to myocarditis) as second-line therapy. Among them, 1 patient received pembrolizumab plus everolimus for 2 months before receiving pazopanib. The 6, 12 and 18-month PFS were 55%, 22%, and 11% respectively. All pts ceased treatment due to eventual PD, and there were no toxicity-related discontinuations. 5 pts subsequently received third-line MKIs, including cabozantinib (3 pts), pazopanib (1 pt), and lenvatinib (1 pt). The pt who received lenvatinib had discontinued it as first line therapy due to toxicity. The 2 pts treated with third-line cabozantinib and the pt rechallenged with lenvatinib showed no PD at 12-months and no toxicity related discontinuation. Conclusions: Pazopanib was associated with durable PFS and good tolerability when offered after PD or intolerance on lenvatinib in this retrospective analysis, warranting a randomized prospective study. [Table: see text]

641 Background: Tumors of neuroendocrine origin are a rare, heterogenous group of neoplasms. Neuroendocrine neoplasms (NENs) are categorized by site of origin, differentiation status, and by grade (Ki-67 expression and/or mitotic rate), with prognostic variability accordingly. These tumors frequently metastasize to bone, with reported incidence between 6-12% by older SSTR imaging. Our study evaluates patients with well-differentiated tumors of neuroendocrine origin to determine the incidence of osseous metastases when evaluated with higher-sensitivity Ga68 DOTATATE PET scans. The study characterizes the clinical features. Methods: This study was performed at a single, 3-site, US tertiary-care institution. IRB approval was obtained. An automated data extraction tool was used to mine the electronic medical record by searching all positron emission tomography (PET) studies for keywords. Identified scans had to include a combination of the following keywords: “Dotatate” AND “met*” or “lesion” AND “bone” or “osse*” or “skel*”. The individual medical records from the generated report were reviewed to include only patients with 1) well-differentiated NETs of GI and pancreatic origin, lung carcinoid, paraganglioma/pheochromocytoma, or other/unknown primary site, and 2) patients with confirmed osseous metastatic disease. Patient data was entered into a database and evaluated in aggregate. Results: 1,948 PET scans of 1,473 patients were extracted from the EMR, from which 424 patients were identified for inclusion; scans were performed between 5/2018 and 5/2021. Calculated incidence of bone metastasis by Ga68 DOTATATE PET was 28.8%. Median age of included population was 61 years (range 14-92), 49.5% being male. Site of origin was 47.2% bowel NET, 18.9% pancreatic NET, 10.8% lung carcinoid, 10.6% paraganglioma/pheochromocytoma, 2.1% other site, and 10.4% unknown primary. Majority of patients were asymptomatic (64.0%), had sclerotic appearance (76.7%), Krenning 4 (71.4%), and >3 sites (68.3%) of osseous disease. 94.6% of the population had disease of the axial skeleton; 65.6% appendicular. Only 57 patients (13.4%) with osseous disease suffered a fracture, despite metastases at high-risk sites. Fracture occurred at disproportionately low rates in NETs originating in bowel (22.8% of fractures), with proportionately higher rates among pancreatic NETS and paragangliomas/pheochromocytomas (31.6% and 22.8%, respectively). Fractures occurred at proportionately higher rates in higher-grade disease compared to low-grade. Conclusions: Osseous metastatic disease in well-differentiated NENs is evident at much higher rates when imaging with Ga68 DOTATATE PET compared with previously reported data. Nevertheless, fracture occurred at a low rate, suggesting that these patients are at a relatively low risk for skeletal-related events.

e16124 Background: Immune checkpoint inhibitors (ICI) have emerged as a standard treatment option for advanced hepatocellular carcinoma (HCC). Unfortunately, many patients with advanced HCC develop progressive disease on ICI therapy. Furthermore, clinical predictors of response to ICI therapy in HCC are poorly understood. B-catenin mutations are among the most frequent genetic abnormalities in HCC and may provide a mechanism for immune evasion and poor response to ICI (Ruiz de Galarreta, Marina et al. “β-Catenin Activation Promotes Immune Escape and Resistance to Anti-PD-1 Therapy in Hepatocellular Carcinoma.” Cancer discovery 9,8 (2019): 1124-1141. doi:10.1158/2159-8290.CD-19-0074). Methods: We conducted a retrospective cohort study of patients with advanced HCC who were treated with ICI therapy. All patients had ctDNA tumor profiling and were assessed for B-catenin mutation status. Disease status was determined by RECISTv1.1. Median progression-free survival (PFS), 3-month PFS, 6-month PFS, and the disease control rate (DCR) on ICI therapy were compared between B-catenin mutation (BCM) and B-catenin wild-type (BCWT) groups. Results: 15 stage III/IV HCC patients were included in the study. 9 patients harbored BCMs and 6 patients were BCWT. The median PFS in patients with BCM HCC was 4.0 months versus 4.9 months in patients with BCWT HCC. At 3 months, PFS was 56% for BCM HCC compared to 67% for BCWT HCC. Furthermore, the 6-month PFS was 11% for BCM HCC and 50% for BCWT HCC. For best response, 33% of patients with BCM HCC achieved stable disease compared to 67% of patients with BCWT HCC. No patients in our cohort achieved partial or complete response. The DCR for BCM HCC was 33% and the DCR for BCWT HCC was 67%. Conclusions: In patients with advanced HCC, B-catenin mutation status may serve as a potential biomarker of response to ICI therapy. Our data suggests that patients who do not harbor these mutations, have a more durable response to ICI therapy. Further studies are needed to validate these findings.