Siontis, Brittany L.

Abstract Objective To evaluate the clinical value of breast MRI in radiation-associated angiosarcoma of the breast (RAASB) for assessing disease extent at diagnosis and after neoadjuvant therapy compared with clinical examination and surgical pathology. Methods This IRB-approved retrospective study included 25 patients with breast MRIs between1995 and 2020. MRI estimated disease extent was compared to clinical exam and surgical pathology. MRI findings were evaluated for additional disease and impact on clinical management. Agreement between MRI and clinical assessment of disease was evaluated using Cohen’s kappa statistic. Results Baseline MRI demonstrated moderate agreement with clinical disease extent (Cohen’s κ = 0.44; 95% CI, 0.14-0.75). Thirteen of 24 (54%) of MRIs reflected clinical exam, 4/24 (17%) MRIs underestimated disease, and 5/24 (21%) MRIs overestimated disease. Baseline MRI changed surgical management in 4/24 (17%). In 8 patients who proceeded directly to surgery, MRI reflected pathology in 6/8 (75%). In 10 patients with post-neoadjuvant MRI, 4/10 (40%) pathology and MRI extent were similar, 5/10 (50%) MRI overestimated disease, and 1/10 (10%) MRI underestimated disease. Conclusion MRI has clinical value in assessing RAASB with the potential for significantly altering surgical management. In this small cohort, post-neoadjuvant MRI demonstrated limited additional clinical value. Larger studies are needed to define the optimal role and timing of post-neoadjuvant MRI. Advances in knowledge Baseline MRI detected additional disease not identified on initial clinical exam in 5/24 (21%) and changed surgical management in 4/24 (17%). Although baseline MRI demonstrated moderate agreement with clinical examination, post-neoadjuvant MRI frequently overestimated residual disease when compared with final pathology.

Abstract Background: Solitary fibrous tumors (SFT) make up less than 5% of sarcomas. The Demicco model stratifies risk of metastasis based on age, tumor size, mitotic count, and necrosis. Patients (pts) with relapsed disease have limited options. We evaluated outcomes of systemic therapies (tx) to treat SFT. Methods: A retrospective analysis was performed of pts with intermediate-to-high risk SFT confirmed by soft tissue pathologists at a multi-site health system from 1999 – 2024. Demographics, tx, and pt outcomes were analyzed. Radiographic response was abstracted from documentation by treating provider. Results: Sixty pts had intermediate-to-high risk SFT, of which 21 pts received systemic tx. Of these, 12 were male, median age at diagnosis 62.8 years (41.0 – 82.7 yrs). Tumors originated from chest (11, 52.4%), abdomen (5, 23.8%), pelvis (4, 19.0%), and skull (1, 4.8%). All pts had surgery for primary tumor, median size 16.0 cm (7.8 – 43.0), and 14 (66.7%) had surgery at relapse. Eight pts (38.1%) had perioperative radiation therapy (RT); 12 (57.1%) had palliative RT. Five (23.8%) had ablation. Of the 21 pts, 2 (9.5%) had perioperative chemotherapy (chemo). Twenty pts (95.2%) received median 2 lines (1 – 6) of palliative systemic tx (1 pt did not pursue any). One pt had partial response on dacarbazine, otherwise best clinical response was stable disease (SD, 53.1% vascular endothelial growth factor inhibitors (VEGFi), 40% chemo) or disease progression (PD). Most pts received VEGFi: 11 pts had sunitinib (median 3.1 months, range 1.0 – 10.6 mo), 11 pts had pazopanib (4.1 mo, 0.1 – 38.7), and 10 pts had temozolomide/bevacizumab (5.6 mo, 1.0 – 15.8). VEGFi was dose reduced or held in 59.4% . Discontinuation due to toxicity occurred in 34.4% of pts treated with VEGFi vs 26.7% of pts treated with chemo. Five pts received liposomal doxorubicin (median 4.8 mo, range 3.5 – 11.3). Four pts had doxorubicin with dacarbazine, ifosfamide or olaratumab (2.8 mo, 0.7 – 8.5). Two pts received dacarbazine (1.9 and 9.6 mo, respectively), and 2 pts received gemcitabine/docetaxel (0.9 and 4 mo). Eribulin and trabectedin (1 pt, respectively) were used for less than 1 mo. Tx was held or dose reduced for 1 pt on doxorubicin/dacarbazine and 1 pt on gemcitabine/docetaxel. Three pts had immunotherapy (IO, 2 pts pembrolizumab, 1 pt nivolumab/ipilimumab) and stopped for PD (2 pts) or toxicity (1 pt) after 2 mo or less. Two pts participated in clinical trials. Median time from primary surgery to relapse was 2.0 yrs (0.0 – 12.3). Sixteen pts died (76.2%), 14 from SFT. Median time from relapse to death or last contact was 4.1 yrs (0.5 – 14.7). Median overall survival from diagnosis to death/last contact was 6.6 yrs (0.6 – 27.0). Conclusion: Perioperative chemo was rarely used to treat intermediate-to-high risk SFT. For relapse, VEGFi use was more common than chemo, with more pts achieving SD and receiving longer duration of tx. VEGFi had greater toxicity and subsequent discontinuation. No benefit was observed in few pts who received IO. Clinical trial participation was uncommon. Citation Format: Miranda Lin, Brittany Siontis, Steven Robinson, Scott Okuno, Thanh Ho. Systemic Therapy and Outcomes in Patients with Intermediate or High-Risk Solitary Fibrous Tumor [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Breaking Barriers in the Fight against Rare Cancers; 2026 Jul 18-20; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86(14_Suppl):Abstract nr B054.

TPS11598 Background: Fibroblast Activation Protein (FAP) is expressed on the surface of cancer-associated fibroblasts and is involved in the formation, maintenance, and spread of tumors. Sarcoma frequently demonstrates high expression of FAP on the tumor cells themselves in contrast to other solid tumors, where it is mainly expressed on CAFs within the tumor stroma. Radioligand therapies utilizing alpha emitting isotopes such as Ac-225 have emerged as promising treatment strategies across multiple targets and indications in oncology. Ac-225 and its daughter radionuclides emit high-energy alpha particles capable of inducing double-stranded DNA breaks, leading to significant cytotoxic effects within cells. Early clinical data for other Ac-225-labeled compounds have shown promising outcomes, particularly in settings where traditional therapies have failed. [Ac-225] RTX-2358 (Ratio Therapeutics Inc, Boston, MA) is a novel FAP-targeted radioligand designed for specific high-affinity binding, resulting in prolonged tumor residence and limited normal tissue uptake. This sustained tumor retention leads to extended delivery of cytotoxic radiation to FAP-expressing tumors. A beta-emitting analog, [Lu-177]RTX-2358, has been administered to more than 25 patients under the German §13.2b compassionate use framework across multiple tumor types. Longitudinal SPECT imaging performed as late as 14 days after administration demonstrated persistent tumor retention with minimal washout. Based on time–activity curve analysis from these data, tumor biological half-time is estimated to be well in excess of 1,000 hours. Renal clearance was observed to be consistent with that reported for established lutetium-177–labeled radioligand therapies. Methods: This study is a seamless Phase 1 / 2 dose escalation study. The Phase 1 portion consists of a 3 x 3 dose escalation design, with patients treated in 3 planned dose escalation cohorts (7.5, 11.25 and 15 MBq) with up to 6, 8-week cycles of [Ac-225]RTX-2358. Backfill of phase 1 cohorts is permitted to facilitate selection of the recommended administered activity level for the subsequent Phase 2 expansion cohort. Dose escalation / de-escalation decisions will be made by a Safety Review Committee. Patients over 18yrs with a history of histologically confirmed relapsed or refractory soft tissue sarcoma (measurable disease per RECIST v1.1) are eligible if they have a positive [Cu-64]LNTH-1363S FAP PET, an ECOG PS 0 to 1, and adequate organ reserve and renal function. Recruitment of the first cohort was completed in December 2025. The ATLAS Study: NCT07156565 Clinical trial information: NCT07156565 .

11502 Background: To report results from the open-label alveolar soft part sarcoma (ASPS) cohort of the phase III APROMISS trial (NCT03016819) evaluating Catequentinib hydrochloride (AL3818), an oral multitargeted receptor tyrosine kinase inhibitor, in adults with advanced or metastatic ASPS. Methods: Adult patients with pathologic and molecularly confirmed advanced ASPS, either treatment-naive or previously treated (excluding cediranib), were enrolled in the open-label, non-randomized ASPS cohort of the phase III APROMISS trial conducted across the United States, Asia, and Europe. Catequentinib hydrochloride was administered orally at 12 mg once daily in 21-day cycles (14 days on/7 days off) until disease progression, toxicity, or death. The primary endpoint was objective response rate (ORR) assessed per RECIST by Blinded Independent Central Review (BICR) (predefined threshold: 31%). Secondary endpoints included duration of response (DOR) with a predefined target of =/>6 months, progression free survival (PFS) and overall survival (OS). Results: From July 2017 to August 2022, a total of 56 patients entered the trial; 56 patients were evaluable for the primary endpoint. Median (m-) age was 29.5 years (range: 18 – 66), with 24 female and 32 male. Best overall response included 1/56 complete response (1.8%), 14/56 partial responses (25.0%), 36/56 stable disease (64.3%), and 3/56 (5.4%) progressive disease. RECIST ORR by BICR was 26.8% (95% CI, 15.8–40.3); m-DOR was 22.57 months (95%CI: 10.38-NE). The study data was collected close to 8 years for all patients. mPFS was 18.33 months (95% CI, 14.19–23.13), with 6- and 12-month progression-free rates of 88.77% (95% CI, 76.68–94.79) and 65.54% (95% CI, 50.42–77.06), respectively. mOS was 59.27 months (95% CI, 44.09–NE), with 6- and 12-month overall survival rates of 94.64% (95% CI, 84.30–98.24) and 90.81% (95% CI, 79.30–96.08), respectively. Overall, 27/56 (48.2%) patients experienced grade ≥3 treatment-related adverse events, most commonly diarrhea (50.0%), hypertension (44.6%), fatigue (37.5%), nausea (35.7%), and palmar-plantar erythrodysesthesia syndrome (30.4%); one patient (1.8%) had a grade 5 event (respiratory failure). Conclusions: Catequentinib hydrochloride demonstrated meaningful antitumor activity and durable responses in adults with advanced ASPS. Despite the ORR of 26.8% slightly below the predefined 31% threshold, disease control was prolonged, with a m-DOR exceeding 22 months. Favorable PFS and OS outcomes, together with a manageable safety profile, support its clinical benefit in this ultra-rare sarcoma. Clinical trial information: NCT03016819 .

Background: Localized soft tissue sarcoma (STS) is primarily treated with surgical resection with or without radiotherapy (RT), while the role of chemotherapy (CT) as a radiosensitizer remains unclear. We report our single-institution experience with combined chemoradiotherapy (CCRT) in treating localized STS. Methods: We conducted a retrospective analysis of patients with localized STS treated at Mayo Clinic with mitomycin, cisplatin, and doxorubicin (MitoAP) concurrently with RT between 1/1/85 and 12/12/19. Results: We identified 179 patients (median age 58 years; median tumor size 9.5 cm), with 83.8% of tumors located in the extremities or trunk. Among them, 77.1% received perioperative CT in addition to CCRT, with 95% of those treated in the neoadjuvant setting. Median RT dose was 50 Gray. The 5-year disease-specific survival (DSS) was 77.9% (95% confidence interval, CI: 70.8–83.4%). The addition of perioperative CT to CCRT was associated with improved DSS compared with CCRT alone (p = 0.01, Hazard Ratio, HR: 0.48, 95% CI: 0.27–0.85). Median post-CCRT tumor viability was 30% and did not differ by CT use (p = 0.39), but varied significantly by histology (p < 0.001). Conclusions: Our institutional protocol utilizing two cycles of MitoAP with RT was well tolerated. DSS in our cohort was similar to historical data using perioperative RT alone, suggesting no clear benefit from CCRT. However, the majority of patients in our cohort were classified as high risk, which may have attenuated a potential survival benefit in the absence of appropriate comparative controls. Furthermore, additional perioperative CT to CCRT was associated with improved DSS and differential histology-specific responses in tumor viability, suggesting that a more aggressive neoadjuvant and perioperative approach may be beneficial in selected patients.

Physician burnout is prevalent and contributes to the high number of physicians choosing to leave clinical practice. The field of hematology-oncology (HO) poses unique challenges for trainees and staff physicians who have to deliver bad news, manage complicated psychosocial situations, deal with the limited ability to prolong life, and juggle multiple time-sensitive demands from coworkers, patients, and families. Furthermore, they often face the death of their patients, along with its emotional toll on patients’ families and the physicians themselves. Burnout in HO is prevalent and increasing, with many physicians reporting in several studies that they plan to reduce working hours and/or retire early. The demand for hematologists and oncologists is rapidly rising, but in the setting of a worsening HO workforce shortage and an increasing number of patients with cancer. Therefore, it is imperative to develop strategies to mitigate or address burnout in HO physicians to improve well-being and prevent attrition. Herein, we describe risk factors and causes of physician burnout in HO trainees and practicing physicians in the United States, with a focus on institutional and individual strategies to address this issue. We also provide recommendations to address the burnout epidemic from the HO standpoint.

Background: Myxofibrosarcomas are notoriously highly infiltrative soft-tissue sarcomas, making negative surgical margins difficult to obtain. Recently, vacuum-assisted closure (VAC) is used to delay wound closure until a negative margin has been achieved; however, this can delay care and increase costs. Our institution has historically performed single-stage resections with intraoperative frozen margin analysis and reconstruction in these patients. The purpose of this study is to report the outcomes of this technique. Methods: We reviewed 112 patients (62 males, mean age 70 ± 14 years) with superficial myxofibrosarcoma. Eighty-eight patients received preoperative radiation. All patients underwent surgical resection with intraoperative frozen margin analysis, and the planned reconstruction was performed in a single anesthetic. Results: The 10-year local recurrence-free survival was 90%; positive intraoperative frozen section (HR 7.44, p = 0.004) and final permanent margins (HR 8.53, p = 0.007) were associated with local recurrence. Intraoperative margins were negative in 103 (92%) of patients, 1 of which was positive on final permanent section. There were nine cases of microscopically positive margins, of which seven underwent immediate re-excision to a negative margin. The accuracy of frozen margin assessment for myxofibrosarcoma was between 92.92 and 98.23%. All patients underwent reconstruction at the time of resection, with 19% needing an additional procedure, most commonly due to a wound complication (12%). Conclusions: Multidisciplinary single-stage excision with intraoperative frozen margin assessment and soft-tissue reconstruction yields low rates of local recurrence in patients with superficial myxofibrosarcoma.

11506 Background: Catequentinib Hydrochloride (AL3818, Anlotinib, Catequentinib) is a novel, orally administered, small molecule tyrosine kinase inhibitor. There remains an unmet need for effective, well tolerated therapies for patients (pts) with advanced/ metastatic leiomyosarcoma (LMS). We performed a randomized, double blind trial of Catequentinib monotherapy versus placebo in advanced/metastatic LMS. Methods: Patients with a diagnosis of LMS requiring third or further line treatment were eligible. Catequentinib was administered in a 21-day cycle with 14 days on and 7 days off regimen. In this double blind phase 3 trial, patients were randomized 2:1 to Catequentinib or placebo, with the option of crossover to Catequentinib after confirmed Progression Disease (PD) on placebo. Progression-free survival (PFS) with Log Rank test was the primary endpoint and the trial was conducted at multiple sites in the US, UK and EU. Results: Total N = 111 patients were enrolled, and N = 110 were treated and evaluated, 74 randomized to Catequentinib (C), and 36 to placebo (P). In arms (C)/(P) median ages were 59.0/60.5 (range: 33-91) years respectively and 59/29 (79.7%/80.6%) were female. Median PFS by Blinded Independent Central Review (BICR) met the primary endpoint at 3.42 months (95% CI: 2.60, 6.83) for (C) and 1.41 months (95% CI: 1.35, 4.86) for (P) with a p-value of 0.0265 and a HR of 0.536 (95% CI: 0.307, 0.936). Median PFS for patients stratified at ≤ 3 prior lines was 4.86 months (95% CI: 2.04, 8.94) for (C) and 1.41 months (95% CI: 1.31, 4.86) for (P) with a p-value of 0.0046 and a HR of 0.386 (95% CI: 0.196, 0.760). The 6-month progression-free rate was 42.37% for (C) and 20.71% for (P). OS was 17.45 months (95% CI: 13.57, 19.32) for (C) and 16.33 months (95% CI: 11.27, NE) for crossover patients in the (P) arm. 30 (40.5%) of patients have experienced grade 3 treatment-related adverse events in the (C) arm compared to 3 (8.3%) of patients in the (P) arm. The most common TEAE for (C) vs (P) were diarrhea (50.0% vs 22.2%), stomatitis (31.1% vs 8.3%), fatigue (64.9% vs 41.7%), and hypertension (47.3% vs 19.4%). Conclusions: This phase 3 trial met the primary PFS endpoint and demonstrates superior PFS for Catequentinib vs placebo in metastatic/advanced LMS. This study confirms the acceptable benefit-risk profile of Catequentinib in LMS. Catequentinib is an effective and well tolerated treatment option for patients with LMS. Clinical trial information: NCT03016819 .

3046 Background: Prior work has shown that detection of circulating tumor DNA (ctDNA) at time of diagnosis of leiomyosarcoma (LMS) is associated with lower likelihood of objective response and patients with detectable ctDNA after two cycles of chemotherapy have worse survival. However, because ctDNA exists at much lower concentrations in plasma compared to cell-free DNA of non-tumor origin, the sensitivity of these prognostic measures to tumor signals remains unclear. With increasing evidence of ctDNA fragments being shorter than the background non-tumor cell-free DNA, we sought to test whether restricting our analysis to smaller fragment sizes would improve detection of ctDNA in LMS. Methods: Plasma was serially collected from patients with LMS undergoing chemotherapy. Cell-free DNA extracted from these samples was profiled by ultra-low-passage whole-genome sequencing (ULPWGS). Copy number alterations were identified and used to detect ctDNA using the ichorCNA algorithm before and after restricting the dataset to fragments of 90-150bp (short). We compared detectability of ctDNA via ichorCNA between analyses using all sequencing data and those using data restricted to short fragments. Results: From 28 patients, 126 plasma samples were profiled. The median fragment length of cell-free DNA was 240bp (IQR 142-349) for patients with LMS, compared to 307bp (IQR 171-465, p < 0.001) in samples collected from healthy controls. Short fragments made up 19.48% of LMS libraries at diagnosis when ctDNA levels were highest, 15.27% of all LMS samples, and 12.96% of libraries from healthy controls. While ctDNA was detectable by ULPWGS in 17% of all samples, detection increased to 40% when analyzed using only short cell-free DNA fragments (p < 0.0001). The proportion of diagnostic samples with detectable ctDNA was nominally higher when analyzed by short fragments (39% vs. 64% with 90-150bp size restriction, p = 0.1078, n = 28) and was significantly higher in samples collected after two cycles of chemotherapy (5% vs. 40% with 90-150bp size restriction, p = 0.0197, n = 20). Increases in ctDNA detectability with fragment size restriction were also observed in each of localized and metastatic subgroups (metastatic: 16% without restriction, 38% with restriction, n = 97, p = 0.0012; localized: 17% vs. 45%, n = 39, p = 0.04). Conclusions: Our results demonstrate that detection of ctDNA is improved by analyzing short fragments of cell-free DNA in samples collected from patients with LMS. These findings represent a potential to increase the sensitivity of an affordable, low-coverage liquid biopsy assay and may enhance the prognostic value of ctDNA detection in these patients. Further study of the association between ctDNA detection and outcome is needed to fully validate the impact of fragment size restricted analysis of cell-free DNA samples in patients with LMS and is currently ongoing in a prospective study.

In the INTRIGUE phase III trial (ClinicalTrials.gov identifier: NCT03673501 ), adult patients with advanced gastrointestinal stromal tumor previously treated with imatinib were randomly assigned 1:1 to ripretinib 150 mg once daily or sunitinib 50 mg once daily (4 weeks on/2 weeks off). In the primary analysis, overall survival (OS) was immature. In this study, we report the final planned analysis of OS (key secondary end point), progression-free survival (PFS) on third-line therapy (second PFS; prespecified exploratory end point), and long-term safety. Final OS analysis was prespecified to occur with approximately 200 and ≥145 events in the overall and KIT exon 11 intention-to-treat (ITT) populations, respectively. As of March 15, 2023, there were 211 and 151 OS events in the overall ITT and KIT exon 11 ITT populations, respectively. Median OS was similar between second-line ripretinib and sunitinib in both populations (overall, 35.5 v 31.5 months; KIT exon 11, 35.5 v 32.8 months). Median second PFS (on third-line therapy) for the overall ITT population was similar between the ripretinib and sunitinib arms (7.7 v 7.4 months). Safety was consistent with the primary analysis. OS from this analysis was similar between arms, and second PFS suggests that receiving ripretinib did not adversely affect the PFS of third-line therapy.