MT-5111: This phase I/II is investigating the appropriate dose level and effectiveness of a new cancer drug (MT-5111) in people with HER2-positive solid cancersA Phase 1 Open-label, Multicenter Dose Escalation and Expansion Study of MT-5111 in Subjects With Previously Treated Advanced HER2-positive Solid Tumors

Inclusion

1. Histologically confirmed, unresectable, locally advanced or metastatic solid cancers:

   • Part A (Dose-Escalation): All HER2-positive solid cancers are eligible
   • Part B (Dose-Expansion): Any type of HER2-positive solid cancer, including breast cancer, and gastric or gastroesophageal adenocarcinomas (GEA).
2. HER2-positive in the latest tumor sample tested for HER2 (testing to be done on a metastatic lesion in cases of metastatic cancers).
3. Relapsed or refractory to or intolerant of existing therapy(ies)
4. At least 1 measurable or evaluable lesion according to RECIST 1.1 (Subjects with evaluable disease only may be included in the dose escalation phase)
5. ECOG performance score of ≤ 1

6. Adequate Bone marrow function as determined by:

   • Absolute neutrophil count (ANC) ≥ 1,000/mm3
   • Platelet count ≥ 75,000 mm³ and
   • Hemoglobin ≥ 8.0 g/dL
   • Red blood cell transfusion within 2 weeks of study treatment start is allowed if hemoglobin levels remain stable

7. Kidney function:

   • Creatinine clearance (CLcr) ≥ 50 mL/min either measured or estimated using the Cockcroft-Gault formula

8. Cardiac Function:

   • Left ventricular ejection fraction (LVEF) ≥ 55% on the echocardiogram (ECHO) assessment (preferred), or multigated acquisition (MUGA) scan, and QTcF ≤ 480 ms for women and QTcF ≤ 450 ms for men [average from three QTcF values on the triplicate 12-lead electrocardiogram (ECG)] at baseline

9. Hepatic function:

   • Total bilirubin ≤ 1.5 x ULN, or ≤ 3 x ULN for subjects with Gilbert's Syndrome and
   • AST ≤ 3 x ULN (or ≤ 5 x ULN if liver metastasis) and ALT ≤ 3 x ULN (or ≤ 5 x ULN if liver metastasis)