[68Ga]Ga-DOTA-GSI PET/CT (Granzyme B PET/CT)

This study plans to enroll 30 patients with locally advanced or metastatic triple-negative breast cancer (TNBC) who are scheduled to receive at least two cycles of a regimen containing an immune checkpoint inhibitor (ICI). All ICI treatments must be administered in accordance with current clinical indications. For patients who intend to participate in a clinical trial involving an ICI, they must meet the eligibility criteria of that specific trial protocol. After screening and enrollment, participants will undergo a \[68Ga\]Ga-DOTA-GSI PET/CT (Granzyme B PET/CT) scan before initiating the ICI-containing regimen and again after Cycle 2 (C2). Participants will continue the ICI regimen until disease progression, with tissue biopsies performed as needed. By integrating patients' baseline clinical characteristics, treatment outcomes, and prognostic information, this study aims to conduct a comprehensive analysis. The objective is to investigate whether the following factors, as assessed by Granzyme B PET/CT, can serve as early predictors of response to immunotherapy in patients with advanced breast cancer: baseline Granzyme B expression levels, immunotherapy-activated Granzyme B levels after C2, and the heterogeneity of Granzyme B expression at baseline and after C2.