Aptamers and improved aptamers are provided with enhanced efficacy for binding to target molecules in vivo or for treating cancer or other diseases. Such improvements in aptamers are provided that enhance in vivo efficacy such as binding to the target molecule or enhancing anti-cancer activity. Such improvements also include stability to serum nucleases, reduced binding to a soluble form of the target molecule, increased avidity, affinity or specificity to the target molecule on a cell surface, increased lifetime in circulation, or any combination of the foregoing. Improvements are provided by truncation, multimerization, including at least one non-natural nucleic acid, adding a 3′ or 5′ polyethylene glycol, or any combination thereof. Aptamers for treatment of autoimmune diseases are also provided.