SSGJ-705 Monotherapy and Combination Therapy in Advanced HER2-Expressing Solid Tumors

Inclusion Criteria: * Males and/or females over age 18. * Histologically and/or cytologically documented local advanced or metastatic non-Small Cell Lung Cancer（NSCLC），Breast Cancer（BC）or Gastric/Gastroesophageal Junction Cancer （G/GEJC). * Eastern Cooperative Oncology Group (ECOG) performance status of 0-1. * Expected survival \>3 months. * Signed informed consent form. Exclusion Criteria: * Any remaining adverse events (AEs) \> grade 1 from prior anti-tumor treatment as per Common Terminology Criteria for Adverse Events（CTCAE） v5. 0, with exception of hair loss, fatigue, and grade 2 peripheral neurotoxicity. * Pregnant or nursing women or women/men who are ready to give birth. * symptomatic central nervous system metastasis. * Allergy to other antibody drugs or any excipients in the study drugs. * Inadequate organ or bone marrow function.