Phase-II study involves as few as 100 number of study subjects. This phase is designed to closely study and evaluate the efficacy of the gene therapy product for specific ailments and associated side effects in a well controlled manner. The phase-III study follows after the establishment of drug efficacy and involves several hundreds to thousand patients. After successful scrutiny and establishment of the drug as a good candidate license for drug production is issued. Phase-IV is the post marketing stage where the drug is further developed and comparatively analysed.

Gene therapy has evolved in the past decade and a range of new products are being developed to treat disease like cancer, hemophilia and other rare diseases. CBER along with NIH and FDA stringently controls the quality of drug development and the scientific research involved in the gene therapy strategy. The field of gene therapy has given hope for treatment of otherwise incurable diseases and has completely changed the face of medicine. In the coming years let us hope that this field develops to an even greater extent with proper developed specific gene therapy treatments for all heritable, non heritable, congenital, and other incurable diseases.