Citations

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 .

94 Background: Technetium (Tc99m) trofolastat (USANC) is a novel urea-based small molecule SPECT radiotracer with utility in imaging overexpression of PSMA in prostate cancer (PCa). Unlike earlier agents targeting PSMA, this ligand is rapidly internalized and retained in tumors. We conducted an open-label, multicenter phase 2 study in the US and Europe (NCT01667536). An interim analysis was performed at approximately 50% accrual. Methods: Patients (pts) with confirmed adenocarcinoma of the prostate scheduled for RP with EPLND at high risk for disease outside of the prostate gland were eligible. High risk pts were ≥cT3 or Kattan nomogram score ≥130. Within 30 days of screening, pts required a bone scan and pelvic MRI. After enrollment, pts received trofolastat followed by whole-body planar and SPECT/CT imaging 3 to 6 hrs later. Pts then underwent RP with EPLND within 21 days. SPECT/CT images were evaluated centrally by 3 readers blinded to clinical information and compared to on-site pathology assessments using a common scoring template. The primary endpoint was the ability of trofolastat to detect PCa within the gland. Secondary endpoints included detection of extent and location within the gland, pelvic lymph nodes and comparative performance against MRI. Results: 84 pts were enrolled to date from 16 centers. Interim data is available for 54 pts. A majority (≥2/3) of SPECT/CT readers correctly identified the presence or absence of primary PCa in 51/54 (94%, 85-98 95% CI) patients including 2 true-negative cases treated with neoadjuvant enzalutamide. Sensitivity and specificity were 94% (84-98 95% CI) and 100% (34-100 95% CI) respectively. Conclusions: Based on the interim data available, trofolastat has accurately detected primary prostate carcinoma within the gland with high sensitivity and specificity in high-risk pts prior to surgery. Updated results, analyses of secondary endpoints, pelvic lymph nodes, and comparative performance vs. MRI from this ongoing study will be presented. Clinical trial information: NCT01667536. [Table: see text]