Abstract P6-10-03: Datopotamab Deruxtecan (Dato-DXd) in Advanced Triple-Negative Breast Cancer (TNBC): Updated Results From the Phase 1 TROPION-PanTumor01 Study

Abstract 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.