Cancer is a major cause of mortality worldwide, killing about 9 million people each year. Ovarian cancer is one of the ten most common cancers in women, considered the most fatal among gynecological tumors; and prostate cancer one of the most frequent and fatal in men. The detection of these tumor types currently has important limitations, hindering the efficiency of treatment and consequently patient’s survival. Specific molecules produced by tumors could be used as biomarkers and are considered good targets for diagnosis. Thus, the use of aptamers represents an important tool that could be applied to improve specificity in tumor diagnosis and personalized therapy. Aptamers are small, single-stranded synthetic oligonucleotides, capable of binding with high specificity to a molecular target, and are promising due to their unique pharmacokinetic properties: they are not immunogenic and are susceptible to chemical modifications and bioconjugations to nanoparticles, imaging agents and therapeutic drugs. In this way, the application of this technology could generate diagnoses for rapid and preventive detection that improve the life expectancy of patients with ovarian and prostate tumors. The main goal of this project is the creation of a tumor-specific diagnostic method, which differentiates benign, metastatic, and non-metastatic tumors, for application in liquid biopsies and magnetic resonance for ovarian and prostate cancer. In this purpose, the Cell-Selex method was applied for the selection of specific aptamers for each tumor type considering its condition as: benign, metastatic, and non-metastatic. Although the use of this methodology is being explored in several diseases, its application in ovarian and prostate tumors has an innovative character and will contribute to the technological development of public health in Brazil.