Breast cancer is women's most common type of cancer, with a global rate of over 522,000 deaths per year. One of the main problems related to breast cancer relies in the early detection, as the specialized treatment. In this direction was developed, characterized and tested in vivo a smart delivery system, based on radiolabelled magnetic core mesoporous silica doped with trastuzumab as intralesional nanodrug for breast cancer imaging and possible therapy. The results showed that nanoparticles had a size of 58.98.1nm, with specific surface area of 872 m(2)/g and pore volume of 0.85cm(3)/g with a pore diameter of 3.15nm. The magnetic core mesoporous silica was efficiently labelled with 99mTc (97.5% +/- 0.8) and doped >98%. The cytotoxicity assay, demonstrated they are safe to use. The data were corroborated with the IC50 result of: 829.6 mu g +/- 43.2. The biodistribution showed an uptake by the tumour of 7.5% (systemic via) and 97.37% (intralesional) with less than 3% of these nanoparticles absorbed by healthy tissues. In a period 6-h post-injection, no barrier delimited by the tumour was crossed, corroborating the use as intralesional nanodrug.