A Phase II Study to Evaluate the Efficacy and Safety of SKB571 in Recurrent or Metastatic HNSCC Participants

Inclusion Criteria: * Age ≥ 18 and ≤ 75 years at the time of signing the informed consent form. * Histologically or cytologically confirmed recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) that is not curable by local therapy and not amenable to curative surgery, with the primary tumor located in the oral cavity, oropharynx, hypopharynx, or larynx. * Subjects with at least one measurable lesion assessed by the investigator according to RECIST v1.1. * Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 within 7 days before the first dose. * Participants who have adequate bone marrow, liver, kidney, and coagulation function. * Male and female participants must agree to use highly effective methods of contraception during the specified period of the study. * Participants must voluntarily join this study, sign the informed consent form (ICF), and be able to comply with the visits and related procedures specified in the protocol. Exclusion Criteria: * History or current metastases to central nervous system. * Subjects with other malignant tumors within 3 years prior to the first dose. * Presence of any cardiovascular and cerebrovascular disorders or risk factors. * Presence of uncontrolled systemic disease. * Presence of clinically symptomatic or uncontrolled pleural effusion, pericardial effusion, or ascites requiring repeated drainage. * History of interstitial lung disease (ILD) or non-infectious pneumonitis. * Presence within 3 months be…