Haddad, Tufia C.

LBA1551 Background: Traditional cancer therapy is primarily delivered in clinical settings, imposing logistical, emotional, and financial burdens, particularly on rural and underserved patients. While international studies have demonstrated the safety of home-based chemotherapy, no randomized U.S. trials have evaluated this approach. Mayo Clinic’s CCBW program aims to expand access to high-quality cancer care by providing in-home cancer treatment, lab testing, telemedicine, remote patient monitoring, command center and paramedic support. This pragmatic randomized controlled trial evaluates feasibility and impact of home-based versus in-clinic cancer directed therapy on patient preference, acceptability, safety, and patient-reported outcomes. Methods: Adult patients (ECOG 0-2) receiving chemotherapy or hormonal therapy at Mayo Clinic Florida were randomized 1:1 after confirmation of treatment tolerance in clinic to receive (1) home-based care for 24 weeks or (2) in-clinic care for 8 weeks followed by home-based care for 16 weeks. Target accrual is 200 patients. A planned interim analysis after 50 enrollments assessed accrual, data completeness, technical challenges, safety, and study outcomes. The primary endpoint is patient ratings of their overall cancer care experience (0–10 scale, CAHPS Cancer Care Survey) at 8 weeks. 200 patients provide 80% power to detect a 0.45 standard deviation difference in mean ratings between arms with a 2-sided 2-sample t-test (α=0.05) and 20% missing data rate. Secondary endpoints are patient preference, comfort with home infusions, treatment worthwhileness, functional/symptom assessments (EORTC QLQ-F17, PRO-CTCAE, GP5), grade ≥3 AEs, hospitalizations, and overall survival. Cost is a tertiary endpoint. The trial is IRB-approved (#23001719) and registered (NCT05969860). Results: Enrollment began 8/23/23. As of 2/21/25, 52 patients (26 per arm) were enrolled and 36 started protocol treatment. Common cancers were breast (38%), colorectal (21%), prostate (19%), and multiple myeloma (14%). 64% (28/44) of patients were female; 84% identified as White, 14% as Black, and 2% as multiple races. Median distance to clinic was 20 miles (range 2-66). After 8 weeks, patients in both arms rated their overall cancer care experience highly (mean [SD]=9.69 [0.85] versus 9.54 [0.66] for home-based vs. in-clinic care, n=26). After 24 weeks, 73% preferred home-based care, 18% had no preference, and 9% preferred in-clinic care; 100% felt comfortable with home infusions. No grade ≥3 AEs related to location of care have occurred. Conclusions: Early findings support the feasibility, safety, and high patient acceptability of home-based cancer therapy. No safety concerns related to care location were observed and most patients preferred home-based treatment. Ongoing accrual and analysis will assess clinical outcomes and cost implications. Clinical trial information: NCT05969860 .

e14545 Background: Next generation sequencing (NGS) identifies genomic alterations in DNA obtained from tissue biopsies and/or blood [circulating tumor (ct)DNA]. We anticipate a lower rate of copy number loss (CNL) in ctDNA compared to tissue, as lower ctDNA tumor fraction may limit the ability to detect a deletion. However, we observed several instances of a CNL in ctDNA that was not identified in a tissue specimen, prompting this systematic evaluation of an institutional dataset. We focused on BRCA1/2 pathogenic variants (PVs) given their therapeutic implications and coverage across testing platforms. Methods: Using an IRB-approved protocol, we evaluated an institutional repository of NGS results performed across the Mayo Clinic Enterprise. We focused on patients (pts) who had both tissue and blood NGS testing performed. We further narrowed this cohort to those with a BRCA1/2 PVs, somatic and/or germline, as determined by testing performed at Guardant Health, Tempus, or Foundation Medicine. We abstracted information about each variant, including type of alteration classification and functional impact. Demographic information, cancer characteristics, and germline testing information was collected. Fisher’s exact test was used to compare alteration frequencies in ctDNA vs tissue using GraphPad Prism v 10.1. Results: From Dec 2015-Sept 2024, we identified 158 unique pts with BRCA1/2 PV who had NGS results for both tissue and ctDNA. The median age at first reporting BRCA1/2 variant was 67 years (range: 29-98 years). 48% of pts were female, and the most common cancer type sites were lung (23%), colorectal (20%), and pancreaticobiliary (20%). We identified 198 unique pathogenic genomic alterations; 71 in BRCA1 & 127 in BRCA2 . Most common alteration was an SNV or indel (127/198), followed by CNL (n = 63), splice site variants (n = 5), fusions (n = 2), and rearrangements (n = 1). Of the 126 SNV or indels, 50 (39.7%) were identified in both ctDNA and tissue, 40 (31.7%) were detected in blood only, 36 (28.6%) identified only in tissue (p < 0.0001). Amongst the 63 CNL, only 3 (4.8%) were identified in both ctDNA and tissue; 41(65.1%) were only identified in ctDNA, and 19 (30.2%) in tissue only (p < 0.0001). In the 19 tissue-only CNL tests, 12/19 noted one or more additional pathogenic SNV/Indel in BRCA1/2. In the 41 ctDNA-only CNL tests, 1/41 noted one or more additional pathogenic SNV/Indel in BRCA 1/2 . Germline testing was available in 41/63 pts with copy number loss. 3/41 deletions were identified in germline (2 in ctDNA, 1 in tissue). Conclusions: We observed a low degree of concordance in CNL between tissue and ctDNA for BRCA1/2 . CNL detection in ctDNA that could not be confirmed in germline or with a second alteration warrants further attention. In particular, clinicians should be cautioned when interpreting ctDNA reports noting BRCA1/2 CNL without clarity if this represents biallelic loss or a synchronous loss of function.

TPS1125 Background: Despite the many available treatments for patients (pts) with HR+, HER2– recurrent/metastatic breast cancer (MBC), optimal treatment after progression on CDK4/6 inhibitors (CDK4/6i) is unclear. One possible CDK4/6i resistance mechanism is increased expression of Aurora kinase A (AURKA), a key mitosis regulator associated with poor prognosis. Further implicated in CDK 4/6i resistance, high c-Myc or RB1 loss of function (LOF) are associated with transcriptional co-regulation or synthetic lethality, respectively, with AURKA. Alisertib is a highly selective, reversible, ATP-competitive, orally administered, small-molecule AURKA inhibitor with antiproliferative activity in HR+ BC-derived cell lines and BC xenograft models. Models with elevated AURKA or c-Myc expression, or RB1 LOF show greater alisertib sensitivity. Alisertib had activity in phase 1 and 2 trials, including objective response rates (ORRs) of 19.6–20% and median progression-free survival (PFS) of 5.4–5.6 months alone or with fulvestrant in pts with HR+/HER2–, endocrine-resistant MBC. The most common treatment-related grade ≥3 adverse events (AEs) were neutropenia, anemia, and leukopenia. Methods: ALISCA-Breast1 (NCT06369285) is a randomized phase 2 study. Primary objective: to determine the optimal alisertib dose administered with endocrine therapy (ET) based on AEs and serious AEs per CTCAE v5.0 and efficacy (ORR, duration of response, disease-control rate, PFS, overall survival). Secondary objectives: to identify biomarkers of efficacy and alisertib pharmacokinetics (PK). Key inclusion criteria: ≥18 years; ECOG performance status 0 or 1; confirmed HR+, HER2–, recurrent/metastatic breast adenocarcinoma not amenable to curative therapy; available tumor tissue for biomarker analyses; progression on or after ≥2 prior ET lines in recurrent/metastatic setting; prior CDK4/6i with ET in recurrent/metastatic setting. Key exclusion criteria: prior chemotherapy in recurrent/metastatic setting; prior AURKA-specific or pan-Aurora-targeted agents; unstable brain metastases. Eligible pts will be randomized 1:1:1 to alisertib 30 mg, 40 mg, or 50 mg orally twice daily on days 1−3, 8–10, and 15–17 every 28 days, plus physician’s choice of anastrozole, letrozole, exemestane, fulvestrant, or tamoxifen not previously used in recurrent/metastatic setting or progressed upon in adjuvant setting; ≤50 pts will be enrolled per arm in the USA and Europe. All pts will undergo sparse PK sampling. Tumor tissue will be centrally assessed for biomarkers, including RB1, MYC, TP53, ESR1, PI3K/AKT pathway, HER2 and AURKA genomic alterations/expression levels. The study will determine the optimal alisertib dose to combine with ET and may identify biomarker(s) defining pts with the greatest benefit from alisertib-based therapy. Clinical trial information: NCT06369285 .

e13622 Background: Chimeric antigen receptor T-cell (CAR-T) therapy has revolutionized treatment of hematologic malignancies; however, severe toxicities like cytokine release syndrome (CRS) remain a limitation to broader utilization. Using a large dataset of patients treated with CAR-T, we developed a machine learning (ML) model leveraging multi-model patient characteristics to predict the risk of CRS onset with clinically meaningful lead times. Methods: A prospectively maintained dataset of CAR-T patients treated at Mayo Clinic was used. Baseline disease/patients characteristics, labs, ECG, echocardiogram, and vital signs (including data from remote patient monitoring program) were collected. A 24-hour rolling window was used to generate daily averages, maximum, minimum, and deltas for each parameter. ECG and echocardiogram data were forward-imputed; vital signs and labs were not imputed. Each day-post-infusion served as a potential event (CRS onset vs. no CRS). A gradient boosting classifier was trained and tested on a subset of patients (n = 351) using 1,000 bootstrap iterations, evaluating 24-, 48-, and 72-hour lead times. Shapley-based feature importance guided simplification to an 11-feature model, externally validated on an independent cohort (n = 51). Models’ performance assessed using the area under the receiver operating characteristic curve (AUC). Results: A total of 402 patients treated with CAR-T were examined. Median age was 64 years and 36% were female. Primary diagnosis was B-cell lymphoma (n = 240) or multiple myeloma (n = 162). A total of 226,332 vital sign measurements and 372,871 lab values, as well as ECG and echocardiogram data, were collected for 30 days post-infusion. Overall, 79.8% of patients experienced CRS within 30 days. The full ML model demonstrated AUCs of 0.90 (95% CI 0.86–0.93), 0.83 (95% CI 0.77–0.88), and 0.82 (95% CI 0.77–0.87) for 24-, 48-, and 72-hour predictions of CRS, respectively. Including “day of CRS onset post CAR-T” as a feature improved the 72-hour AUC to 0.87 (95% CI 0.83–0.90). A model restricted to vital signs alone showed AUCs of 0.88, 0.75, and 0.71 for 24-, 48-, and 72-hour horizons. An 11-feature model—focusing on temperature, blood pressure, fibrinogen, CRP, serum sodium level, QRS interval, and lymphocyte counts—maintained high accuracy at 24 hours (AUC 0.90, 95% CI 0.86–0.93) and was validated externally using an independent dataset with an AUC of 0.92. Conclusions: Our ML model provides a reliable approach for predicting if/when CRS will occur, with up to three days of lead time before clinical manifestation, offering an opportunity for proactive management. The robust performance of a parsimonious 11-feature model supports practical adoption across clinical settings and real-time risk stratification to enhance patient safety. Prospective validation and integration into clinical workflows will be critical to translating these findings into practice.

e13551 Background: The landscape of cancer care is evolving rapidly. In 2023, there were 83 new FDA oncology approvals, and 145 interventional treatment (tx) studies opened across Mayo Clinic. We are exploring novel precision outreach approaches utilizing an LLM-integrated chatbot application to “ping” patients (pts) with specific clinical or genomic characteristics about newly available drugs or clinical trials. As novel outreach methods are considered, we surveyed a patient (pt) support group to understand communication preferences and awareness of adjuvant CDK4/6 inhibitors in tx of breast cancer (BC). Methods: On October 7, 2024, we administered a cross-sectional survey to 41 members of the Breast Cancer Support Network (BCSN) in Rochester, MN as a part of an IRB exempt quality improvement project. Leaders of the BCSN shared information to all participants, noting that the survey’s intent was to represent the pt voice and participation was voluntary. Anonymous survey data were collected with descriptive results reported. Results: 34/41 participants in the BCSN shared demographic information. The majority (83%) were > 50 years of age. 47% reported stage I BC, 12% stage II, 6% stage III, and 35% were unsure of their stage. Most participants (26/34, 76%) reported that their BC was hormone receptor positive (HR+), 2 HER-2 positive, and 6 unsure of their BC receptor status. 24/26 (92%) of pts with HR+ BC were taking or planning to start adjuvant endocrine therapy. 10/34 (29%) were aware that adjuvant CDK 4/6 inhibitors were approved. Of these 10 participants, 2 learned of it from online health resources, 6 from their clinician, 1 from social media, and 1 from a support group. The majority (66%) were unsure if they qualified for these drugs. Regarding receipt of information on new drug approvals/tx options, the highest ranked communication preference was to receive this information in person at an upcoming visit (ranked 1st by 50% of participants), followed by EHR-based message (28%), email (10%), phone call (6%), letter (4%), or an interactive chatbot (0%). Most respondents noted that communication from their healthcare provider was very important (30/37, 81%), with others stating that this was somewhat important (5/37, 14%) or neutral (2/37, 5%). Most noted that receiving information about tx options via video or visual aid before a visit would be very helpful (33/41, 80%). When asked about follow up after learning of a new drug approval, 17/32 (53%) of pts preferred an appointment, 9/32 (28%) a phone call, 3/32 (9%) a decision aid tool, and 3/32 (9%) a questionnaire to assess their understanding. Conclusions: Providing personalized, timely communication about new FDA approved tx options is important for BC survivors and critical for improving care delivery. While technological solutions could broaden awareness, this requires balancing pt preferences for direct communication with clinicians.

529 Background: Neoadjuvant chemotherapy (NAC) is commonly administered to patients (pts) with estrogen receptor alpha (ER) negative (immunohistochemistry [IHC] 0%) and ER-low (IHC 1-10%) breast cancer (BC). For pts without pathological complete response (pCR), ER expression may differ between baseline and residual BC following NAC. We previously demonstrated adjuvant endocrine therapy (ET) omission in ER-low early-stage BC was associated with significantly worse overall survival (OS); however, this effect was restricted to pts with residual BC following NAC and those with higher baseline ER levels (IHC 6-10%) (Choong et al., ASCO 2024). Here, we assessed how often ER was expressed in residual invasive BC for pts treated with NAC for ER-negative and ER-low BC. Methods: Weidentified pts with pre-treatment (tx) ER-negative and ER-low (regardless of HER2 expression) stage I-III BC treated with NAC who underwent BC surgery at Mayo Clinic Rochester between 2009 and 2023. ER IHC was performed in a CAP/CLIA laboratory. We evaluated ER expression in residual invasive BC for pts without pCR. The percent of pts with a post-tx change in ER status was estimated and reported with 95% Wilson confidence intervals. Results: 955 pts (838 [88%] pre-tx ER-negative; 117 [12%] pre-tx ER-low) met inclusion criteria, of whom 69% had HER2-negative and 31% HER2-positive BC. The median age at diagnosis was 52 (range: 24-86). 496 (52%) had residual BC. Residual BC was more common in HER2-negative versus (vs) positive tumors (56% vs 42%, p < 0.001) but did not differ significantly by ER status (ER-negative 51% vs ER-low 57%, p = 0.22). Of those with residual BC, 277/496 (56%) had ER re-testing. Rates of ER re-testing did not vary for pre-tx ER-negative vs -low (57% vs 51%, p = 0.37) but were significantly lower for HER2-positive vs HER2-negative tumors (39% vs 62%, p < 0.001). Among those with post-tx testing, 31/277 (11%, 95% CI: 8-15%) had an increase in ER expression from pretreatment levels (defined as ER IHC < 1% to either 1-10% or > 10%; or ER IHC 1-10% to > 10%). In these 31 pts, the original NAC was for either TNBC (21/31; 68%) or HER2+ BC (10/31; 32%). In pts with pre-tx ER-negative BC, 27/243 (11%, 95% CI: 8-16%) had ER expression in the residual BC including 14/243 (6%, 95% CI: 3-9%) with ER > 10% and 13/243 (5%, 95% CI: 3-9%) with ER 1-10%. For pts with baseline ER-low BC, 4/34 (12%, 95% CI: 5-27%) had ER > 10% in the residual BC. Among the 31 pts where ER increased following NAC, 21/31 (68%) received adjuvant ET, including 17/18 if ER was > 10% in the residual disease and 4/13 in those with ER 1-10%. Conclusions: In pts treated with NAC for ER-negative or ER-low BC not achieving pCR, we identified higher ER expression in the residual breast cancer in > 10% of pts. Given that omission of ET in ER-low BC with residual cancer following NAC is associated with worse survival, repeat biomarker testing should be considered in those without pCR, and ET individualized according to ER expression.

526 Background: The PALLAS trial (NCT02513394) investigated the efficacy of the addition of palbociclib (palbo) to standard adjuvant endocrine therapy (ET) to reduce breast cancer recurrence. Previous analyses of this trial have not shown significant benefit of combination palbo+ET over ET alone. Given prior data showing that extent of neutropenia is associated with response to palbo and other cell cycle-specific therapies, we evaluated whether extent of neutropenia could identify responders to palbo in the adjuvant setting. Methods: PALLAS is a global, open-label, phase III trial that randomized patients (pts) with stage II-III hormone-receptor positive, HER2-negative breast cancer to receive ET for ≥5 years with or without standard-dose palbo for 2 years in 28-day cycles. The primary endpoint is invasive disease-free survival (iDFS). For this exploratory analysis, the palbo population was classified into pts with treatment-emergent high-grade neutropenia (HGN) with maximum grade ≥3 (absolute neutrophil count <1000), or low-grade/no neutropenia (LGN) with maximum grade <2; these groups were compared to each other and to the ET alone group for 5-year iDFS outcomes. Logistic regression examined individual baseline characteristics associated with HGN during the first 3 cycles within the palbo group. Impact of HGN during the first 3, 6, and 12 cycles on iDFS was tested using univariate and multivariable landmark Cox regression. Results: The safety population included 5736 pts, 2840 allocated to palbo+ET, 2896 to ET alone. Prior publications reported no new safety signals, low rates of serious infection, and no grade 5 treatment-related events. The palbo+ET group consisted of 1006 (35.4%) LGN and 1834 (64.6%) HGN. 5-year iDFS results are shown in the table. Pts who received palbo+ET and developed HGN by the end of cycle 6 had significantly improved 5-year iDFS compared to those who received ET alone (p=0.04), which remained statistically significant when adjusting for body mass index (BMI), prior chemotherapy, and race. Multivariable logistic regression showed lower BMI, prior chemotherapy, Asian race, and prior mastectomy were significantly associated with HGN (all p<0.05). Conclusions: In this exploratory analysis of the phase III PALLAS adjuvant trial, addition of palbo to ET appeared to be superior to ET alone in pts who developed HGN in the first 6 cycles of treatment but not in those who had LGN. These findings are consistent with observations in the metastatic setting suggesting that neutropenia could be a useful biomarker for palbo concentration and efficacy. Clinical trial information: NCT02513394 . Maximum grade neutropenia measured at end of cycle: 5-year iDFS Palbo+ET HGN (%) Palbo+ET LGN (%) ET alone (%) Hazard Ratio p-value 3 84.9 84.4 1.06 0.54 84.9 82.9 1.17 0.06 6 85.6 84.9 1.08 0.44 85.6 83.4 1.19 0.04 12 86.3 85.9 1.06 0.57 86.3 85.0 1.12 0.20

e13893 Background: For individuals with CNS tumors who have experience difficulties with in-person (IP) evaluations due to disease-related neurologic disability or the costs associated with travel, telehealth (TH) offers a convenient and timely alternative for accessing specialized neuro-oncology care. We report our institution’s experience with telehealth utilization in neuro-oncology. Methods: We conducted a retrospective review of patients who had at least one neuro-oncology telehealth visit between August 2021 and May 2024 at Mayo Clinic in Rochester, Minnesota. Reasons for visits, outcomes of appointments, acute care utilization following visits was reviewed. Results: A total of 660 patients who had at least one TH visit between August 2021 and May 2024 were included in the analysis. Median age was 56 (range 20-98), 49% were female, and 92% were white. Most patients resided in the US Midwest (84%), followed by the South (8%), West (5%), Northeast (1%), and US Territories (< 1%). Less than two percent were international patients. The most common primary visit diagnosis was glioblastoma (GBM, 26%), followed by astrocytoma, IDH-mutant (17%), meningioma (17%), oligodendroglioma, IDH-mutant, 1p/19q codeleted (7%). Of 6657 visits reviewed, 2745 (41%) were conducted via TH. Telehealth visits served various purposes, including consultation for newly diagnosed tumors or abnormal MRIs (n = 26), second opinion for an established tumor diagnosis (n = 119), discussion about clinical trial participation (n = 108), tumor-related treatment discussions (n = 719), chemotherapy education (n = 161), new symptom assessment (n = 117), symptom management (n = 366), and tumor surveillance (n = 1694). Outcomes from telehealth visits included enrollment in clinical trials (n = 28), proceeding with tumor-directed surgery (n = 46), initiation of radiation therapy (n = 88), starting or changing systemic therapy (n = 377), continuing existing systemic therapy (n = 932), transition to supportive care (n = 45), tumor diagnostic workup (n = 28), continuation of tumor surveillance (n = 1254). Acute care utilization, defined as an emergency department visit or hospitalization within one month of an appointment, was the same following telehealth visits compared to in-person visits (6.9% for IP vs 5% for TH, p = 0.507). Conclusions: Our findings demonstrate that telehealth can effectively support all aspects of neuro-oncology care, ranging from initial diagnosis discussions to systemic therapy management and transitions to supportive care. Telehealth offers a convenient and accessible method of care delivery option for patients faced with neurologic illness. Additionally, THs do not lead to increased acute care utilization compared to IP evaluations.

e13891 Background: Most patients with central nervous system (CNS) malignancy develop cognitive impairment, fatigue, and mood-related symptoms that are impacted by cancer and treatment, including radiation therapy. We currently have limited therapies to mitigate neurocognitive toxicity. It is important to accurately assess neurocognitive function and symptom burden when working to establish therapeutics. The objective of this trial is to assess the effectiveness of therapies aimed at improving neurocognitive function and quality of life by leveraging a decentralized approach incorporating an established digital neurocognitive assessment tool and development of a remote symptom collection/medication log to improve capture of longitudinal neurocognitive data. Methods: This is an open-label decentralized clinical trial (NCT06377696) that randomizes patients who have received intracranial radiation for primary and secondary brain tumors in a 1:1 allocation to health promotion with a wearable device +/- metformin (targeting radiation-related toxicity). Remote symptom collection is reported through digital patient surveys. Medication adherence is being monitored through a digital medication log developed for the study. Remote neurologic examination is performed by clinical neuro-oncologists at telehealth visits. Participants perform serial remote cognitive assessments with an established digital neurocognitive testing platform – Mayo Test Drive (MTD). Cognitive assessments and symptom surveys were designed to be completed on a smartphone, tablet, or computer device. Results: The study started enrollment on May 31, 2024. As of January 27, 2025, 54 of 100 planned participants have enrolled (27 on each arm). 51 participants remain active on trial; 3 withdrew from trial participation (2 prior to treatment, 1 after treatment). The overall completion rate for a quality-of-life questionnaire (EORTC QLQ-C30) is 85.0%, and each dose of metformin logged is 78.5%. The overall completion rate for virtual neurologic examination and short test of mental status is 94.7%. For MTD, the overall completion rate is 97.9%. The average MTD session duration was 16 minutes. Most participants completed MTD testing using a smartphone (90.5%) at home (89.1%). Conclusions: These results provide preliminary support that a decentralized trial assessing neurocognitive outcomes is feasible in patients with CNS malignancy. The completion rates of questionnaires and objective cognitive evaluation are comparable or higher than expected with historic norms. Final study results will provide real-world cognitive and quality-of-life data for patients with CNS tumors while providing preliminary data on the effectiveness of device-based health promotion +/- metformin for treatment related cognitive decline. Clinical trial information: NCT06377696 .

e13890 Background: Many oncology practices have reported continued use of telemedicine since onset of the COVID-19 pandemic. However, the future sustainability of telemedicine within oncology practices remains unclear, particularly because federal policies that enabled adoption in response to the public health emergency (PHE) have not been made permanent. Understanding similarities and differences in telemedicine utilization at high-volume oncology centers is crucial for shaping evidence-based policy that enables equitable access to oncology care across varying geographies. Methods: This is a cross-sectional, year-over-year, retrospective cohort analysis of trends in telemedicine utilization across all medical oncology clinical appointments conducted among adult patients (age >18) from January 2019 to December 2023 at Stanford Medicine Cancer Center (SM) – comprising multiple campuses in the California Bay Area – and the Mayo Clinic Comprehensive Cancer Center (MC) – a multiregional cancer practice with tertiary referral campuses in Minnesota, Florida, and Arizona, as well as community-based clinics throughout the Upper Midwest. Results: Both institutions exhibited a similar trend in telemedicine adoption over time. This was characterized by an initial surge in utilization following the PHE declaration in March 2020, followed by sustained utilization rates from 2021 to 2023. However, telemedicine use as a proportion of the overall practice differed significantly between institutions. At SM, the rate of telemedicine visits as a proportion of overall clinical practice was 60.3% (49,136/ 81,502) in 2021, 59.9% (52,247/ 87,215) in 2022, and 57.2% (55,007/ 96,163) in 2023. At MC, the proportion of telemedicine utilization was 12.8% in 2021 (23,873/186,086), 14.7% in 2022 (28,985/196,777), and 14.0% in 2023 (30,208/215,941). Deployment in the setting of new versus return visits also differed between institutions. In 2023, telemedicine accounted for 53.7% (6,440/11,998) of new and 57.7% (48,567/84,165) of return visits at SM, compared to 15.5% (3,359/21,728) and 13.8% (26,849/194,213) at MC. Additionally, while video visits were the predominant modality used to conduct telemedicine visits at both institutions from 2021 onward, in 2023 phone visits still made up 17.9% (5,394/30,208) of all telemedicine visits at MC, compared to just 5.4% (2,990/55,007) at SM. Conclusions: Stanford Medicine and Mayo Clinic exhibited a pattern of initial growth of telemedicine adoption in 2020, followed by sustained utilization from 2021-2023. We observed unique differences in the overall proportion, visit type deployment, and modality of telemedicine utilization between institutions. However, this study confirms telemedicine visits have remained a fixture of medical oncology care for many patients at these institutions since the COVID-19 pandemic.