“…Although active targeting seems to be an effective strategy for delivering drugs to tumor sites, the specific molecules highly expressed on tumor cell surface may not be exclusive to tumor cells. 95,171,172 For example, the folate receptor is highly overexpressed in ovarian, lung and breast cancers, and is an excellent drug target. However, folate receptor is also expressed in normal tissues of the choroid plexus, thyroid, colon and bladder, which limits its targeting specificity.…”