This work presents some recent clinical, epidemiological and experimental data on the cancer preventive effect of healthy hormonal equilibrium. Insulin resistance-associated overproduction of peptide hormones, such as growth hormone, insulin and insulin-like growth factors, interacting simply with cell membrane receptors, have a proven tumour inducing capacity. Another group of hormones, including estrogens, thyroids and vitamin D, has both genomic intranuclear and non-genomic membrane-associated receptor signalling, thus they have complex roles in all basic cellular functions. Recent results suggest that defective synthesis of these latter hormones or alterations of their signal transduction pathways may thoroughly disturb metabolic processes, reproduction and the regulation of cell proliferation. Primary cancer prevention based on the preservation or restoration of the hormonal and metabolic equilibrium of patients may be the main program of the anticancer fight in the 21st century. Moreover, in cases with diagnosed malignancy, we should cure the ill patients instead of their tumours. After surgical tumour removal, the achievement of hormonal and metabolic equilibrium restores the natural defence mechanisms of patients, which may help to stop tumour recurrence.