ST-1703

Phase I Dose escalation phase Main purpose: To evaluate the safety and tolerability of ST-1703 tablets in patients with HER2-positive advanced malignant solid tumors who have failed standard treatment, and to explore the maximum tolerated dose (MTD) of ST-1703 tablets. Secondary purpose: 1) To evaluate the pharmacokinetic (PK) characteristics of ST-1703 tablets; 2) To preliminarily evaluate the anti-tumor efficacy of ST-1703 tablets. Phase IIa Main purpose: To evaluate the efficacy of ST-1703 tablets in patients with HER2-positive advanced breast cancer (including brain metastases from breast cancer) and other HER2-positive advanced malignant solid tumors (such as gastric cancer, colorectal cancer, biliary tract cancer, lung cancer, esophageal cancer, ovarian cancer, salivary gland cancer, bladder cancer, and brain glial cell cancer, etc.). Secondary purpose: 1) To further evaluate the pharmacokinetic (PK) characteristics of ST-1703 tablets; 2) To further evaluate the safety and tolerability of ST-1703 tablets.