It is well known that cancer is defined as a group of diseases that differ both regarding the tissues they affect as well as their origin. For this reason, much effort is being made in the development of new drugs with the aim of increasing survival and patients' quality of life. There is already a wide spectrum of anti-cancer agents that follow different mechanisms of action, such as the inhibitors of topoisomerases I and II and anti-mitotic chemicals, among others. Usually, these drugs are able to increase the patient's survival, although their toxicity worsens the patient's quality of life. Therefore, we should seriously consider alternative mechanisms, as well as the co-administration of these drugs with non-toxic compounds, such as melatonin or retinoic acid. This would increase the toxic effects of these drugs at low doses. Obviously, a better understanding of modified physiological systems during the development of these diseases would improve the diagnostic tools. This would be translated, in turn, into a higher survival index. The alteration of the proteolytic enzymes involved in the renin-angiotensin system and in the regulation of the gonadotrophins and TRH synthesis in breast cancer are examples of the above. These two proteins are regulated by the same enzyme, pyrrolidon carboxipeptidase, and both are directly involved in the initiation and development of breast cancer. Therefore, the aim of the present review is to revise the different options available at present to improve patients' survival and to show alternative mechanisms that may be beneficial to patients' well being.