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Background Metastatic melanoma is the leading cause of skin cancer-related deaths, with a five-year survival rate of only 30%. Myeloid derived suppressor cells (MDSCs) are considered a key driver of metastatic progression and strongly associated with poor outcomes in patients. Central to their pro-tumorigenic and immunosuppressive functions, is increased production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs). Myeloperoxidase (MPO), a myeloid-lineage restricted enzyme, is a major source of ROS and NETs. This study evaluates the contribution of myeloperoxidase (MPO) in melanoma metastasis.Methods Tumors were resected approximately 3 weeks post subcutaneous tumor cell injection. Metastatic burden were quantified using a bioluminescence reporter stably expressed in B16F10 melanoma cells. Metastatic burden was evaluated in C57BL/6J wild-type, syngeneic myeloperoxidase-deficient, and peptidyl arginine deiminase 4-deficient mice, as well as C57BL/6J wild-type mice treated with an MPO-specific inhibitor or hydroxychloroquine. Inhibitor treated mice were also treated with an anti-CD20 antibody to evaluate B cell involvement. At experimental endpoint, 4 weeks post-surgical resection of primary subcutaneous tumor, metastatic tumor burden was quantified by ex vivo bioluminescence imaging, flow cytometry was performed on metastatic sites, and MDSCs were isolated from metastatic sites for T and B cell suppression assays and pico green NETs quantification.Results Targeting MPO significantly reduced lung, inguinal lymph node, and bone metastases compared to untreated wild-type controls. Similarly, NET deficiency and inhibition significantly reduced metastasis suggesting that the anti-metastatic effects of MPO inhibition are mediated, at least in part, through suppression of NETs. MPO/NET deficiency and inhibition significantly reduced CD11b+Ly6G+ MDSCs but increased B cells within metastatic sites, as assessed by flow cytometry. Ex vivo assays revealed diminished MDSC-mediated suppression of T and B cells when MPO or NETs were inhibited. Notably, depletion of B cells abrogated the anti-metastatic effects of targeting MPO.Conclusions These findings demonstrate that targeting MPO significantly reduces metastatic burden in a B cell-dependent manner and limits MDSC-mediated pro-metastatic and immunosuppressive functions. This work underscores the therapeutic potential of targeting MPO in combating melanoma metastasis.