The complexity of cancer remains a huge obstacle to achieving an antidote, and as such the disease requires pragmatic strategies for effective treatment. Cancer theranostics is regarded as a promising approach for the future treatment of all forms of cancer. With the rapid development of nanotechnology, an intimate combination of therapy and diagnosis by a single delivery system combined with an imaging technique will obviously hold the key to early cancer diagnosis and site-specific treatment. With several biological barriers and physiological constraints, the delivery of nanotheranostics remains a challenge to researchers. A few of these theranostics are under clinical studies while others are still under development. It is expected that theranostic medicines will be fast-tracked from the bench to bedside in the next couple of years. Apparently, the expectation seems impossible unless the major challenges in site-specific delivery can be efficiently managed. Herein, we seek to offer a detailed discussion of the challenges involved in the major delivery systems employed in cancer theranostics. This review also provides specific techniques or strategies that can be used to overcome these difficulties.

Keywords: theranostics, biological barriers, physiological constraints, nanotheranostics, site-specific delivery