MMP9 and neoplasm: At present, many tumor-specific binding peptides have been identified, such as RGD and NGR peptide (targeting to tumor vasculature), peptide CRRHWGFEFC (targeting to tumor microenvironment matrix metalloproteinases 9), YEQDPWGVKWWY peptide (targeting to tumor associated macrophages) (Ndinguri et al., 2012; Cieslewicz et al., 2013; Saw and Song, 2019).