Experts reveal the intended outcome of this anticipated clinical trial will determine the safety, tolerability, and maximum tolerated dose (MTD) of MT-5111, a 55 kilodalton protein that de-immunizes ETB targeting HER2+ solid tumors, in patients with advanced disease.

Zev A. Wainberg, MD, Professor of Medicine, University of California, Los Angeles, and colleagues will share information about this study, currently in the enrollment phase, at the ASCO Annual Meeting. In the trial, patients will be given MT-5111 over 30 minutes through IV infusion on days 1, 8, and 15 of each 21-day cycle, in patients with HER2-positive tumors, until signs of reason to withdraw are present.

In regard to phase 1 of this first-in-human, open-label, dose escalation and expansion study, MT-5111 monotherapy in patients with HER2-positive solid tumors will be evaluated. "While the primary objective of this phase will be to determine MTD, secondary objectives include pharmacokinetics, tumor response & immunogenicity" -Dr Wainberg et al noted.

Part 1 of this clinical study entails MT-5111 dose escalation in patients with any HER2+ solid cancers and evaluable diseases, while part 2 will evaluate MT-5111 at the MTD in ≤98 patients via 3 expansion cohorts: HER2+ breast cancer, HER2+ gastric or gastroesophageal junction adenocarcinomas. It is reported all patients in part 2 must have ≥1 measurable lesion per Response Evaluation Criteria in Solid Tumors v1.1.

"In metastatic cases, HER2 positivity must be demonstrated on metastatic lesions. Furthermore, patients with HER2+ breast cancer should have previously had ≥2 lines of HER2-directed therapy; patients with HER2+ GEA should have received or displayed signs of intolerance to trastuzumab therapy," explained lead investigator Zev A. Wainberg, MD, Professor of Medicine at UCLA and co-director of the UCLA GI Oncology Program, and colleagues.

"Immunohistochemistry status must be 2+ or 3+, regardless of in situ hybridization results. Investigators report that if IHC is unavailable for patients with breast cancer or  or GEA, ISH criteria per the American Society of Clinical Oncology College of American Pathologists guidelines will be used," they continued. -Alexis Hyams

Wainberg ZA, Mita MM, Barve MA. A phase I open-label study to investigate safety and tolerability, efficacy, pharmacokinetics, pharmacodynamics, and immunogenicity of MT-5111 in patients with HER2-positive tumors. Presented at: the 2021 ASCO Annual Meeting; June 4-8, 2021; virtual. Abstract TPS258.