Efficacy and Safety Study of Disitamab Vedotin + RC148 vs. Albumin-Paclitaxone ± Toripalimab in HR-/HER2-low Breast Cancer

Inclusion Criteria: * Voluntarily agree to participate in the study and sign the informed consent form * Stage III unresectable locally advanced or Stage IV metastatic breast cancer. * Subjects must be willing and able to provide a tumor tissue block and/or unstained pathology slides, with priority given to the most recent metastatic lesions that have not previously been subjected to radiotherapy. If this is not feasible or available, then a tumor tissue block (or fresh tissue sections) obtained from locally recurrent lesions should be provided. Freshly obtained tissue is preferred over archived tissue. The provided tissue will be used for biomarker testing and must be suitable for analysis of HER2 expression and PD-L1 expression * Invasive breast tumor tissue has been confirmed as HER2 low expression by the central laboratory * Invasive tumor tissue is negative for hormone receptors (HR), defined as immunohistochemistry (IHC) testing showing that the proportion of cells with positive nuclear staining for both ER and PgR in invasive cancer is less than 1%. For patients with weakly positive ER/PgR (1% to 10% of tumor cell nuclei positive), those who are not suitable for endocrine therapy after thorough evaluation by the investigator, and with approval from the sponsor after communication, may be included in this study * For HR-negative, HER2-low expressing unresectable locally advanced or metastatic breast cancer: locally recurrent and unresectable or previously untreated metastatic breast cancer; or those who have completed curative treatment (excluding radiotherapy) (e.g., the date of surgery for the primary breast tumor or the last date of adjuvant therapy administration, whichever is later), with an interval of ≥6 months from the first documented local or distant disease recurrence. For subjects who received taxane drugs during the (neo)adjuvant therapy phase, there must be an interval of ≥12 months from the last taxane administration * ECOG performance status of 0 or 1 * According to the RECIST v1.1 criteria, there must be at least one measurable lesion (for lesions that have previously been irradiated, if the lesion can be measured according to the RECIST v1.1 criteria and there is evidence of significant progression after radiotherapy, the lesion can be considered a target lesion) * Expected survival of at least 12 weeks * Hematologic and organ function criteria to be met within 7 days prior to the first dose of study medication (with normal values based on the clinical trial center's standards, and no blood transfusions, hematopoietic growth factors, albumin, or blood products within 14 days prior to the test): Hemoglobin ≥ 90 g/L Absolute neutrophil count (ANC) ≥ 1.5 × 10\^9/L Platelet count ≥ 100 × 10\^9/L Total bilirubin ≤ 1.5 × upper limit of normal (ULN) or direct bilirubin ≤ ULN (for subjects with total bilirubin \> 1.5 × ULN). Total bilirubin ≤ 3 × ULN (for subjects with Gilbert's disease) Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN or ≤ 5 × ULN (if liver metastases are present) International normalized ratio (INR), prothrombin time (PT), and activated partial thromboplastin time (APTT) ≤ 1.5 × ULN Creatinine clearance (CrCl) calculated by the Cockcroft-Gault formula ≥ 40 mL/min, or serum creatinine ≤ 1.5 × ULN Urine routine test shows urine protein \< 2+; if urine protein ≥ 2+, the 24-hour urine protein quantification result must be \< 1 g. * Female subjects of childbearing potential who meet the following conditions: A serum pregnancy test (with a minimum sensitivity of 25 mIU/mL or equivalent units of β-human chorionic gonadotropin \[β-hCG\]) must be negative within 7 days prior to the first dose of study intervention. Subjects with a false-positive result that is confirmed not to be pregnant are eligible to participate in the study. Must agree to use contraception during the study and for at least 6 months after the last dose of study medication. No breastfeeding or egg donation within 6 months. If sexual activity could lead to pregnancy, they must use at least one acceptable form of contraception from the time of informed consent until at least 6 months after the last dose of study medication. * Male subjects of childbearing potential who meet the following conditions: Must agree to abstain from donating sperm from the start of the study until at least 6 months after the last dose of study medication. If having sexual intercourse with a person of childbearing potential that could lead to pregnancy, must consistently use at least one acceptable form of contraception throughout the study and for at least 6 months after the last dose of study medication. If having sexual intercourse with a pregnant or breastfeeding partner, must use condoms from the time of informed consent until at least 6 months after the last dose of study medication. * Capable of understanding the trial requirements and willing and able to comply with the trial and follow-up procedures. Exclusion Criteria: * Having previously received anti-HER2 treatment, including ADC (Antibody-Drug Conjugates). * Having previously received immunotherapy, including anti PD-(L)1 or anti PD-(L)2 drugs, or drugs that directly target another stimulatory or co-inhibitory T-cell receptor (such as CD137, CTLA-4, OX-40) during the locally advanced or metastatic stage (except if the last administration was ≥12 months prior to recurrence or progression, using \[neo\]adjuvant anti PD-(L)1). * Excluding subjects with brain metastases or leptomeningeal metastases. Subjects with treated brain metastases (surgery and/or radiotherapy) are eligible for inclusion if they meet the following criteria: Subjects who have received treatment for brain metastases may be considered for participation in this study if they have not experienced disease progression as determined by imaging studies within 4 weeks prior to the first dose of study treatment. They must have discontinued the use of co