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Background: Datopotamab deruxtecan (Dato-DXd) is an antibody-drug conjugate (ADC) consisting of a humanized anti-TROP2 IgG1 monoclonal antibody covalently linked to a highly potent topoisomerase I (Topo I) inhibitor payload via a stable, tumor-selective, tetrapeptide-based cleavable linker. Dato-DXd demonstrated compelling single-agent antitumor activity in heavily pretreated patients (pts) with metastatic triple-negative BC (Krop, SABCS 2021). This is the first report of results from the TROPION-PanTumor01 study in pts with unresectable or metastatic hormone receptor–positive (HR+)/human epidermal growth factor receptor 2–negative (HER2−; including HER2-low and HER2-zero) BC. Methods: TROPION-PanTumor01 (NCT03401385) is a phase 1, multicenter, open-label, 2-part dose-escalation/expansion study evaluating Dato-DXd in previously treated pts with solid tumors. Based on previous clinical findings and exposure-response results from pts with NSCLC, Dato-DXd 6 mg/kg IV Q3W is being evaluated in pts with unresectable or metastatic HR+/HER2− BC that progressed on standard therapies. The primary objectives were safety and tolerability. Tumor responses, including ORR (complete response [CR] + partial response [PR]) and DCR (CR + PR + stable disease [SD]), were assessed per RECIST version 1.1 by blinded independent central review. Results: As of the April 29, 2022, data cutoff, 41 pts had received Dato-DXd (median follow-up, 10.9 mo [range, 7-13]); 9 pts were ongoing. The primary cause of treatment discontinuation was disease progression (63%; progressive disease [PD] or clinical progression). Median age was 57 y (range, 33-75); 54% had de novo metastatic disease. Pts were heavily pretreated (Table) with a median of 5 (range, 3-10) prior regimens in the advanced setting; 95% had prior CDK4/6i (adjuvant/metastatic). Median time from initial treatment for metastatic disease to the first dose of Dato-DXd was 42.7 mo (range, 10.2-131.1). Treatment-emergent adverse events (TEAEs; all cause) were observed in 98% (any grade) and 41% (grade ≥3) of pts. Most common TEAEs (any grade, grade ≥3) were stomatitis (80%, 10%), nausea (56%, 0%), fatigue (46%, 2%), and alopecia (37%, 0%). Serious TEAEs were observed in 6 pts (15%); 1 pt died due to dyspnea, which was not considered to be treatment related. Dose reductions occurred in 5 pts due to stomatitis (n=3), fatigue (n=2), keratitis (n=1), and decreased appetite (n=1) (>1 AE per pt); 14 pts had treatment delayed due to stomatitis (n=8), retinopathy (n=1), dysphagia (n=1), fatigue (n=1), malaise (n=1), COVID-19 (n=1), cellulitis (n=1), urinary tract infection (n=1), decreased lymphocyte count (n=1), and nasal congestion (n=1; >1 AE per pt). Three pts discontinued treatment due to keratitis (n=1) and pneumonitis (n=2); 1 case of pneumonitis was adjudicated as grade 2 drug-related interstitial lung disease. The ORR was 29% (11 confirmed PRs; 1 pending confirmation), the DCR was 85% (35/41), and the clinical benefit rate (CR + PR + SD ≥6 mo) was 41% (17/41). Conclusions: Dato-DXd demonstrated a manageable safety profile and encouraging antitumor activity, with high disease control in heavily pretreated pts, the majority having received prior CDK4/6i. Based on these findings, the TROPION-Breast01 (NCT05104866) randomized phase 3 study comparing 2L+ Dato-DXd vs investigator’s choice chemotherapy is currently enrolling pts with HR+/HER2− BC. Prior Therapies in the Adjuvant or Metastatic Setting Citation Format: Funda Meric-Bernstam, Ian Krop, Dejan Juric, Takahiro Kogawa, Erika Hamilton, Alexander I. Spira, Toru Mukohara, Takuya Tsunoda, Senthil Damodaran, Jonathan Greenberg, Wen Gu, Fumiaki Kobayashi, Hong Zebger-Gong, Yui Kawasaki, Rie Wong, Aditya Bardia. PD13-08 Phase 1 TROPION-PanTumor01 Study Evaluating Datopotamab Deruxtecan (Dato-DXd) in Unresectable or Metastatic Hormone Receptor–Positive/HER2–Negative Breast Cancer (BC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD13-08.

Background: Datopotamab deruxtecan (Dato-DXd) is an antibody-drug conjugate (ADC) consisting of a humanized anti-TROP2 IgG1 mAb covalently linked to a highly potent topoisomerase I (Topo I) inhibitor payload via a stable, tumor selective, tetrapeptide-based cleavable linker. Dato-DXd has previously shown encouraging activity in heavily pretreated patients (pts) with metastatic TNBC (Krop, SABCS 2021). Here we report updated results from the TROPION-PanTumor01 study in pts with advanced/metastatic TNBC. Methods: TROPION-PanTumor01 (NCT03401385) is a phase 1, multicenter, open-label, 2-part dose-escalation/expansion study evaluating Dato-DXd in previously treated pts with solid tumors. Based on previous clinical and exposure-response results from pts with NSCLC, Dato-DXd 6 mg/kg IV Q3W is being evaluated in pts with advanced TNBC that relapsed/progressed on standard therapies; 2 pts received 8 mg/kg prior to selection of 6 mg/kg. The primary objectives were safety and tolerability. Tumor responses, including objective response rate (ORR; complete response [CR] + partial response [PR]) and disease control rate (DCR; CR + PR + stable disease [SD]), were assessed per RECIST v1.1 by blinded independent central review. Results: As of April 29, 2022, 44 pts received Dato-DXd (median follow-up, 16.6 mo [range, 13-22]) at the time of data cutoff. The primary cause of treatment discontinuation was disease progression (86%; PD or clinical progression), and 4 pts are still receiving therapy. Median age was 53 y (range, 32-82); 32% had de novo metastatic disease. Pts were heavily pretreated with a median of 3 (range, 1-10) prior regimens in the metastatic setting. Prior treatments included taxanes (91%), anthracyclines (75%), capecitabine (61%), platinum (52%), immunotherapy (43%), Topo I inhibitor–based ADC therapy (32%), and PARPi (18%). Treatment-emergent adverse events (TEAEs; all cause) occurred in 100% (any grade) and 50% (grade ≥3) of pts, respectively. Most common TEAEs (any grade, grade ≥3) were stomatitis (73%, 11%), nausea (66%, 2%), vomiting (39%, 5%), fatigue (34%, 7%), and alopecia (36%, 0%). One pt had grade 3 decreased neutrophil count; no cases of interstitial lung disease (ILD) or grade ≥3 diarrhea were observed. Serious TEAEs were reported in 9 pts (20%); no deaths associated with adverse events (AEs) were observed. Dose reductions occurred in 8 pts (18%) due to stomatitis (n=3), fatigue (n=2), dry eye (n=1), retinal exudates (n=1), and dysgeusia (n=1); 12 pts (27%) delayed treatment due to stomatitis (n=5), dry eye (n=1), keratitis (n=1), blurred vision (n=1), fatigue (n=1), bronchitis (n=1), skin infection (n=1), musculoskeletal chest pain (n=1), dysgeusia (n=1), chronic obstructive pulmonary disease (n=1), and dyspnea (n=1; >1 AE per pt). One pt (2%) discontinued treatment due to grade 1 pneumonitis (which was centrally adjudicated as not ILD). ORR in all pts was 32% (1 CR, 13 PRs), DCR was 80% (35/44), and clinical benefit rate (CR + PR + SD ≥6 mo) was 34% (15/44). Median duration of response was not yet reached; median progression-free survival (mPFS) was 4.3 mo (95% CI, 3.0-7.3), and median overall survival (mOS) was 12.9 mo (95% CI, 10.1-14.7). In the subset of pts without prior Topo I inhibitor–based ADC therapy and with measurable disease at baseline, ORR was 44% (12/27). Among all pts without prior Topo I inhibitor–based ADC therapy (n=30), mPFS was 7.3 mo (95% CI, 3.0-NE), and mOS was 14.3 mo (95% CI, 10.5-NE). Conclusions: Dato-DXd continues to demonstrate encouraging and durable antitumor activity, along with a manageable safety profile, in heavily pretreated pts with metastatic TNBC. Based on these findings, the phase 3 randomized TROPION-Breast02 (NCT05374512) trial comparing Dato-DXd vs chemotherapy as 1L therapy for pts with metastatic TNBC is currently underway. Citation Format: Aditya Bardia, Ian Krop, Funda Meric-Bernstam, Anthony W. Tolcher, Toru Mukohara, Aaron Lisberg, Toshio Shimizu, Erika Hamilton, Alexander I. Spira, Kyriakos P. Papadopoulos, Jonathan Greenberg, Wen Gu, Fumiaki Kobayashi, Hong Zebger-Gong, Yui Kawasaki, Rie Wong, Takahiro Kogawa. Datopotamab Deruxtecan (Dato-DXd) in Advanced Triple-Negative Breast Cancer (TNBC): Updated Results From the Phase 1 TROPION-PanTumor01 Study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-03.

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4078 Background: REG, a multikinase inhibitor, and PEMBRO, an anti-PD-1 mAb, are approved as monotherapies in advanced HCC after progression on sorafenib. This phase 1b dose-finding study investigated first-line REG plus PEMBRO in advanced HCC. Methods: Patients (pts) in the first cohort received a starting REG dose of 120 mg/day orally for 3 weeks (wks) on/1 wk off, which could be escalated (160 mg) or reduced (80 mg) in later cohorts, plus a fixed dose of PEMBRO 200 mg IV every 3 wks. Due to a high dose modification rate in the REG 120 mg cohort, an exploratory REG 80 mg cohort was introduced. Primary objective was safety and tolerability; secondary aims were to assess the maximum tolerated dose (MTD), recommended phase 2 dose, and anti-tumor activity. Results: 35 pts started on REG 120 mg/day and 22 on REG 80 mg/day. Median age was 66 yrs (range 29–81), 84% of pts were male, 70%/30% had ECOG PS 0/1, 26%/74% were BCLC stage B/C, 100% were C–P A, 46% had extrahepatic spread, and 32% had macrovascular invasion. MTD of REG was 120 mg/day. Grade (Gr) 3/4 treatment-emergent adverse events (TEAE) occurred in 86% of pts on REG 120 mg and 50% on REG 80 mg (Table). Most common Gr 3/4 TEAE for REG 120 mg/80 mg were AST increased (23%/9%), lipase increased (20%/5%), ALT increased (17%/9%), and hypertension (17%/9%). TEAE led to REG/PEMBRO dose reductions or interruptions in 71%/57% of pts on REG 120 mg and 59%/45% on REG 80 mg. Median treatment duration (range) was 3.0 months (mo; 0.2–20.5) for REG 120 mg and 3.5 mo (0.03–24.4) for PEMBRO, and 3.5 mo (0.7–10.8) for REG 80 mg and 3.5 mo (0.8–11.3) for PEMBRO. Of 32 evaluable pts on REG 120 mg, 10 (31%) had a partial response (PR) and 18 (56%) had stable disease (SD); disease control rate (DCR) was 88% (RECIST v1.1). Of 22 pts on REG 80 mg, 4 (18%) had a PR and 16 (73%) had SD; DCR was 91%. As of 17 Dec 2020, 16 pts remain on treatment (REG 120 mg n = 5; REG 80 mg n = 11); median follow up was 11.7 mo and 6.9 mo, respectively. REG pharmacokinetic exposure was as expected for 80 mg and 120 mg doses. Flow cytometry analysis of sequential peripheral blood showed changes in subsets of T-cells and monocytes, which may contribute to clinical benefit. Conclusions: First-line REG plus PEMBRO in advanced HCC showed no new safety signals and encouraging anti-tumor activity (DCR ̃90%). The REG 80 mg cohort appeared to have lower rates of dose reductions and interruptions due to TEAE vs REG 120 mg. Efficacy data for the REG 80 mg cohort are preliminary due to short follow-up. Clinical trial information: NCT03347292. [Table: see text]

e16680 Background: REG is approved for the treatment of pts with HCC who previously received SOR, based on results of the phase 3 RESORCE trial. The REFINE study was designed to evaluate the safety and effectiveness of REG in pts with HCC in real-world practice. Methods: This prospective, observational study aims to recruit 1000 pts with unresectable HCC for whom a decision to treat with REG was made by the treating physician prior to enrollment according to the local health authority approved label. The primary endpoint is the incidence of treatment-emergent adverse events (TEAEs) and dose modifications due to TEAEs (NCI-CTCAE v4.03). Secondary endpoints include overall survival (OS) and progression-free survival (investigator assessed). This interim analysis includes the first 500 pts on study for ≥4 months. Results: Of 500 pts enrolled and observed for ≥4 months, 498 received REG and were evaluable (data cut-off: November 11, 2019). Pts were Child-Pugh A 67%, B 11%, C 1%, and missing/not evaluable 21%. Most pts (98%; n = 490) had received prior systemic therapy; 97% (n = 482) had received prior SOR. REG was second line treatment in 81% of pts (n = 403), third line or higher in 17% (n = 87), and first line in 2% (n = 8). Of the 403 pts who received REG second line, 398 (99%) received prior SOR. Among the 482 pts who received SOR in any prior line, the median duration of prior SOR was 4.8 months (interquartile range 2.5–9.6), 45% (n = 216) had a last daily SOR dose of 800 mg, and 8% (n = 40) had a TEAE leading to SOR discontinuation (SOR-intolerant). OS by treatment line is shown in the Table. Among all treated pts, the most frequent TEAEs (any grade) were hand–foot skin reaction (HFSR; 30%), diarrhea (21%), fatigue (16%), and decreased appetite (14%). In SOR-intolerant pts (n = 40), the most frequent TEAEs (any grade) were diarrhea (25%), HFSR (20%), abdominal pain (15%), and decreased appetite (13%). Conclusions: In this interim analysis of REFINE, most pts received REG second line after SOR versus other lines of therapy. Median OS in this subgroup was longer than OS in RESORCE, but the proportion of censored pts was high. The most common TEAEs were similar to those in RESORCE in both the overall cohort and in SOR-intolerant pts. Clinical trial information: NCT03289273 . [Table: see text]

10507 Background: In pediatric patients with solid tumors, regorafenib demonstrated acceptable tolerability and preliminary anti-tumor activity. This phase 1 study evaluated regorafenib in combination with vincristine/irinotecan in pediatric patients with rhabdomyosarcoma (RMS) and other solid tumors. Methods: Patients with relapsed/refractory tumors received intravenous vincristine (1.5 mg/m2, Days 1 and 8) and irinotecan (50 mg/m2/day, Days 1–5) plus once-daily oral regorafenib (patients 6– < 24 months: 60 mg/m2 escalating to 65 mg/m2; patients 2– < 18 years: 72 mg/m2 escalating to 82 mg/m2) on either Days 1–14 (concomitant dosing) or Days 8–21 (sequential dosing) during each 21-day cycle. As per protocol, at least 50% of patients were required to have RMS. Results: At the time of the cut-off, of 21 treated patients (RMS, n = 12; Ewing sarcoma, n = 5; neuroblastoma, n = 3; Wilms tumor, n = 1), two had concomitant (72 mg/m2) and 19 had sequential (72 mg/m2, n = 6; 82 mg/m2, n = 13) dosing. Median age was 10 years (1.5–17.0). Patients received a median of 3 cycles (1–17); dose reductions of irinotecan occurred in 62% of patients. Grade 3 dose-limiting toxicities were reported in both patients receiving concomitant dosing (peripheral neuropathy and liver injury; pain, vomiting, febrile aplasia) and one patient each in the sequential groups (rash and elevated AST; thrombocytopenia). Concomitant dosing was discontinued. The maximum tolerated dose and recommended phase 2 dose (RP2D) of regorafenib in the sequential combination was 82 mg/m2. The most common grade ≥3 treatment-emergent adverse events were neutropenia (71%), thrombocytopenia (33%), leukopenia (29%), anemia (24%), and ALT increased (24%). The response rate was 38%, including 1 complete (RMS) and 7 partial responders (5 RMS, 2 Ewing sarcoma); 3 of whom had prior irinotecan. Six (4 with alveolar subtype) of 12 patients with RMS had a response. Nine patients (43%) had stable disease (maximum duration 17 cycles). After the cut-off, partial response was reported for two additional patients (1 RMS, 1 Ewing sarcoma). Conclusions: Regorafenib can be combined at its single agent RP2D of 82 mg/m2 with standard-dose vincristine/irinotecan (with appropriate dose modifications) in pediatric patients with refractory/relapsed solid tumors in a sequential dosing schedule. Clinical activity was observed in patients with sarcoma. Clinical trial information: NCT02085148.

542 Background: Regorafenib significantly improved overall survival (OS) versus placebo in patients (pts) with uHCC who progressed on prior sorafenib therapy in the phase 3 RESORCE trial. The multicenter, international REFINE trial was designed to evaluate the safety and effectiveness of regorafenib in uHCC in the real-world setting. Methods: This prospective, observational trial aims to recruit 1000 pts with uHCC for whom a decision to treat with regorafenib has been made by the treating physician prior to enrollment according to the local health authority approved label. The primary endpoint is the incidence of treatment-emergent adverse events (TEAEs) and dose modifications due to TEAEs (NCI-CTCAE v4.03). Secondary endpoints are OS, progression-free survival, time to progression, best overall tumor response, and duration of treatment. Tumor response and progression are assessed per investigator according to local standard. An interim analysis includes the first 500 pts observed for ≥4 months. We report baseline characteristics, starting dose, and treatment duration for the interim analysis. Results: Of 498 pts evaluable for analysis, median age was 67 years (range: 22–91) and 84% were male. 59% were from Asia. Proportions of pts with ECOG performance status 0–1/≥2 were 82%/5% (missing 13%); 67% and 11% of pts had Child–Pugh A and B liver function, respectively (missing/not evaluable 21%). 60% of pts had metastases and 33% had vascular invasion. HCC etiology included hepatitis B 37%, alcohol use 26%, hepatitis C 23%, and NASH 7%. Baseline alpha-fetoprotein levels were < 400/≥400 ng/mL in 44%/26% of pts (missing 31%). The initial regorafenib dose was 160 mg/day (d) in 58% of pts, 120 mg/d in 13%, and 80 mg/d in 28% (8 pts initiated at 40 mg/d). The mean (SD) initial daily dose was 131 mg/d (37). Median duration of treatment was 3.7 months (IQR: 1.9–8.5). Conclusions: In this interim analysis of the observational REFINE study, some differences were observed in the characteristics of pts treated with regorafenib from the phase 3 RESORCE trial, reflecting less stringent inclusion criteria in a real-world study. Efficacy and safety analyses are ongoing. Clinical trial information: NCT03289273.