MPO and breast cancer: To investigate the presence of tumor-associated NETs in different organs, breast cancer clinical samples from a Qilu cohort, including primary tumors, metastases of lymph nodes (LNs), lungs, bone and liver (Supplementary Fig. S1a) were analyzed by immunofluorescence (IF) staining with NET biomarkers MPO and citrullinated histone H3 (Ci-H3).