Malignant hydrothorax and ascitic fluid in advanced breast cancer often arise from metastasis to the lungs, pleura, or liver. Patients with this condition experience rapid disease progression and multidrug resistance, facing limited treatment options. Clinical guidelines offer various therapies based on molecular subtypes; however, their effectiveness can be hindered by prior treatments, patient health, and tumor evolution. Current evaluations of treatment efficacy typically take two cycles, delaying the recognition of ineffective therapies and resulting in unnecessary side effects and costs. Organoid models present a promising solution, accurately replicating tumor structure and cellular diversity compared to traditional methods. These patient-derived models facilitate improved drug sensitivity testing, leading to more personalized treatment plans. In this study, 90 patients diagnosed with metastatic breast cancer accompanied by hydrothorax and ascitic fluid will be recruited. Patient-derived organoids will be used to assess the sensitivity of chemotherapy regimens, including Doxorubicin, Carboplatin, Cyclophosphamide, and Paclitaxel, along with targeted therapies such as Herceptin and Pertuzumab.