There has been a major improvement in our knowledge in the area of molecular genetics in the past 20 years. It has become evident that genetic factors are important in the initiation, progression and prognosis of most diseases. Many studies addressed the issue of tumorigenesis, which provided insight into the molecular basis of the sequencional development of cancer, driven by the accumulation of genomic defects. Most of the neoplasms are genetically heterogeneous, independent pathways and simultaneous tumorigenesis may exist within the same organ. As some mutations exist in benignant and also in malignant conditions, it is an important challenge to define the molecular characteristics of significant versus non-significant lesions. A new form of therapeutic intervention is gene therapy. During the next decade it will likely play an increasing role in clinical practice and particularly in the treatment of cancer.