Recently, the study by Im et
al. focused on blocking the release of extracellular vesicles (EVs) by cancer cells, as a strategy to block metastasis, by deploying a drug repurposing screen. Upon screening the library of FDA approved drugs in breast cancer cells in vitro, the authors reported the ability of the antibiotic Sulfisoxazole (SFX) in inhibiting EV biogenesis and secretion. SFX was also effective in reducing breast primary tumor burden and blocking metastasis in immunocompromised and immunocompetent mouse models. As we seek a compound to block EV biogenesis and secretion in our current in vivostudies, we intended to use SFX and hence performed in vitrocharacterization as the first step. However, treatment of two cancer cells with SFX did not reduce the amount of EVs as reported by the authors.