The present invention describes conjugates of hyaluronic acid (HA) with an antitumor agent (AT) for use in the treatment and/or prevention of brain metastatising tumors. In these conjugates, the conjugation linkage is preferably of covalent type, and may involve any free positions on the hyaluronic acid molecule, in particular the Carbon 6 of the N-acetyl-glucosamine units, the carboxyl group of the glucuronic acid units, the amino group of the deacetylated-N-acetyl glucosamine units, any free hydroxyl groups, etc. The antitumor agent may be chosen among drugs know for antitumor activity, like methotrexate, camptothecin, etc. Pharmaceutical compositions and kits for performing said treatments are also disclosed.
