Sacituzumab govitecan (Trop-2 ADC) for breast cancer that has spread to the brain

Inclusion Criteria:

* At least 18 years old (based on actual age at the time of signing the informed consent form), with no restriction on gender
* Able to understand the study purpose, risks, and benefits, and voluntarily sign the written informed consent form; if the patient has cognitive impairment or is unable to express themselves independently, their legal guardian/authorized agent shall sign after being fully informed, and provide valid authorization documents.
* Have access to complete medical records (including breast cancer primary lesion diagnosis data, brain metastasis diagnosis data, SG treatment records, follow-up data, etc.) in the study collaborating medical institutions/specified medical systems to ensure traceability of treatment processes and outcomes.

Diagnosed with breast cancer via histopathological/cytopathological examination, with the diagnostic report issued by a tertiary hospital or the study-designated pathology center.

* Diagnosed with breast cancer brain metastasis based on meeting any of the following conditions: ① Definitive diagnosis by a physician with associate senior title or above, combining contrast-enhanced cranial magnetic resonance imaging (MRI)/computed tomography (CT) with clinical symptoms and signs; ② Postoperative pathology of brain metastatic lesions confirming breast cancer metastasis; ③ Pathological examination of brain metastatic lesion biopsy specimens confirming breast cancer metastasis.
* No restrictions on the number, size of brain metastatic lesions, presence of meningeal metastasis, or presence of brain metastasis-related symptoms (e.g., headache, limb dysfunction).
* Previous treatment with Sacituzumab Govitecan (SG), with clear medication records (prescription orders, medical orders, pharmacy dispensing records, etc.), and no restrictions on the line of SG treatment, dosage, or treatment cycles (both completion of full-cycle treatment and early discontinuation due to adverse reactions/progression are acceptable).
* No restriction on the start time of SG treatment ; patients currently receiving SG treatment, who have completed SG treatment, or who have discontinued SG treatment due to objective reasons are all eligible.
* Stable vital signs at present, without the following uncontrolled severe conditions: ① Severe infections such as sepsis and severe pneumonia (symptoms relieved and laboratory indicators normalized after anti-infective treatment); ② Epileptic seizures within the past 3 months (or uncontrolled without standardized anti-epileptic treatment); ③ Failure of major organs such as heart, liver, and kidney (e.g., New York Heart Association (NYHA) Class Ⅳ cardiac function, Child-Pugh Class C liver function, chronic kidney disease Stage 5) .
* The patient/guardian can cooperate with study follow-up (outpatient follow-up, telephone follow-up, electronic medical record extraction, etc.), and survival status, disease progression, subsequent treatment, adverse reactions, and other information can be obtained within the expected follow-up period.

Exclusion Criteria:

* Complicated with other primary malignant tumors (excluding breast cancer), and the tumor was in an active stage within the past 5 years (not achieving complete remission or disease-free survival for more than 5 years).
* Unable to cooperate with informed consent or follow-up due to mental illness, cognitive impairment, etc., and without qualified guardian assistance.
* Concurrent participation in other interventional clinical trials (e.g., randomized controlled trials), which may affect data collection and result interpretation of this study.
* Other conditions judged by the researcher to affect study quality or patient safety .