Advances in molecular techniques have revealed that different molecular mechanisms are responsible for the behavior of cancer cells. Molecular alterations play a critical role in both the differential diagnosis of cancer and in the development of targeted therapies. Studies have identified the same potentially targetable mutations across various tumor types, supporting the emergence of tumor-agnostic therapies. To date, five biomarkers have been approved for tumor-agnostic therapy: microsatellite instability (MSI), neurotrophic tyrosine receptor kinase (NTRK) fusion, tumor mutation burden (TMB), BRAF V600E mutation, and rearranged during transfection (RET) fusions. The United States Food and Drug Administration (FDA) has approved pembrolizumab for MSI-high tumors or tumors with a high TMB. Larotrectinib and entrectinib have been approved for the treatment of NTRK gene fusion-positive tumors. Additionally, the combination of dabrafenib and trametinib has been approved for BRAF V600E mutations, and selpercatinib has been approved for RET fusion-positive cancers as of 2022. Positive responses to agnostic therapy, a significant milestone in cancer treatment, depend on the identification of new agnostic biomarkers. Ongoing research is focused on defining additional molecular changes, such as programmed death-ligand 1 (PD-L1), Kirsten rat sarcoma virus (KRAS), neuregulin 1 (NRG1), fibroblast growth factor receptor (FGFR), anaplastic lymphoma kinase (ALK), AKT serine/threonine kinase (AKT), human epidermal growth factor receptor 2 (HER2), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), and breast cancer gene (BRCA), as potential agnostic biomarkers in various cancer types.