Solid tumor diagnosis is now entering an era in which molecular genetics plays an important role. Clinical trials have shown different responses to various therapies that correlate with molecular alterations. Biological determinants related to treatment response markers aimed at individualized therapies are being defined and implemented. Patients are now being treated based on the profile of molecular genetic alterations in individual tumors. Protocols based on molecular markers will increase the chances for cure by opting for the right management approach. They also will improve, in most situations, the quality of life of patients with cancer, for example by facilitating organ preservation strategies. The molecular characterization therefore has an important prognostic and practical role in diagnosis.