Accurate　differentiation　of　benign　and　malignant　breast　tumors　is　paramount　for　establishing　schemes　of　breast　cancer　treatment　and　prognosis.　Here　we　report　a　near-infrared　(NIR)　fluorescence　probe　(YF-1)　with　the　overexpressed　cathepsin　C　(CTSC)　in　metastatic　breast　tumors　as　the　detecting　substrate.　This　probe　allows　accurate　identification　of　malignant　tumor　tissue　specimens　among　tumor　tissue　specimens　with　unknown　properties　in　a　blind　study.　Importantly,　a　series　of　visible　to　NIR　CTSC-activated　fluorescence　probes　based　on　the　same　strategy　realize　effective　identification　of　malignant　tumor　tissues,　suggesting　that　CTSC　could　be　the　specific　identification　substrate　of　malignant　breast　tumors.　Furthermore,　a　hydrophilic　PEG　moiety　is　coupled　into　YF-1,　producing　another　CTSC-activated　NIR　probe　(YF-2).　YF-2　has　excellent　tumor-targeting　capability,　enabling　the　visualization　of　lung-metastatic　breast　tumors.　The　excellent　detection　accuracy　and　construction　versatility　of　CTSC　probes　pave　the　way　for　preoperative　diagnosis　of　malignant　breast　tumors.　Copyright　©　2025　The　Authors,　some　rights　reserved.