**5.5 The application of theranostics in cancer**

Cancer is a serious condition of heterogeneous group of diseases where there is uncontrolled and rapid cell growth. This is because of changes at genetic and/or epigenetic level in patient's body. Current treatment for cancer is chemotherapy, radiotherapy, immunotherapy and surgery.

Chemotherapy is not that much useful as a very low level of concentration of drug reaches the tumor. Moreover there is chances development of resistance during treatment and associated side effects. For example, chemotherapeutic agents known as taxanes have emerged as one of the most powerful classes of compounds to combat cancer, exhibiting a wide range of activity. The tubulin/microtubule complex has been proven to be a clinically useful antitumor target. The examples of chemotherapeutics that act *via* perturbation of tubulin polymerization include paclitaxel (Taxol®), docetaxel (Taxotere®), vinblastine, and discodermolide. First, docetaxel is a semi-synthetic derivative of paclitaxel. Next, vinblastine, unlike the other three compounds that all stabilize microtubules, aggregates tubulin and leads to microtubule depolymerisation. Randomized clinical trials evaluating docetaxel and paclitaxel in a first-line treatment setting for metastatic breast, lung, ovarian, and digestive cancers, as well as in the adjuvant setting for breast cancer, have confirmed that taxanes are leading contributors to the armamentarium of cancer treatments. Paclitaxel is used as a first-line chemotherapy treatment for NSCLC, but patients' acquired resistance becomes a critical problem.

Here nanomedicine is better as it allows molecular targeting to get higher concentrations of drug molecules at targeted site. Studies have been to make sure that required amount of drug reaches the site actively or passively which ensures better therapeutic index.

Few examples of nanomedicine in this context are polymeric micelles, polymerdrug conjugates and liposomes. Whereas traditional small molecular drugs n get eliminated from bloodstream quickly but nanomedicine possess longer half-lives.

Furthermore there is enhanced bioavailability and augmented tumor delivery. In addition to it integration of imaging and nanomedicine helps as diagnostic arm of theranostics. The advantages of using such strategy are immense, that will assist in management of oncogenic conditions with the help of theranostics [30].

Applications of theranostics in medicine include:

