Treat Malignant Ascites Caused by Gastrointestinal or Ovarian Cancer With M701 Bispecific Antibody

Inclusion Criteria: * Able to understand and voluntarily sign the written informed consent form. * Histologically or pathologically confirmed epithelial malignancies, including advanced gastric cancer or colorectal cancer that has failed at least two lines of treatment, or platinum-resistant advanced ovarian cancer, primary peritoneal carcinoma, or fallopian tube carcinoma. * Clinical diagnosis of malignant ascites with a moderate or higher amount of ascites. Moderate or higher is defined as having a volume of ascites ≥1L based on CT assessment or actual drainage of ≥1L. * The time interval between the most recent anti-tumor treatment and the first dose of M701 must meet the following criteria: Intraperitoneal treatment: ≥2 weeks since the most recent intraperitoneal treatment. * Adverse events (AEs) from previous treatments have recovered to grade ≤1 (excluding other AEs deemed by the investigator not to affect the safety of the study drug, such as hair loss). * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-2. Estimated survival time ≥8 weeks. * Organ function levels must meet the following requirements: Hematology: Absolute neutrophil count (ANC) ≥1.5 × 10\^9/L, platelets ≥80 × 10\^9/L, hemoglobin ≥8.5 g/dL, lymphocyte ratio (lymphocyte count/leukocyte count) ≥10% (without transfusion within 14 days). Liver function: Total bilirubin ≤1.5 times the upper limit of normal (ULN), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤…