The pharmaceutical giant AstraZeneca­ is expected to announce this week that its oncology unit in Waltham is collaborating with a Maryland company to develop an innovative cancer therapy. The proposed treatment involves delivering powerful cancer drugs on the backs of gold nanoparticles made by CytImmune, of Rockville, Md., that are so tiny 5,000 of them can fit in the width of a human hair.

At that size, the gold flecks make a particularly good vehicle because they can easily carry other molecules, like cancer drugs. They are also believed safe to use in the body.