While usage patterns varied across countries, certain biomarkers, such as programmed death-ligand 1 expression, EGFR mutations, and ALK fusions in NSCLC, KRAS and NRAS mutations in CRC, estrogen receptor/progesterone receptor status in breast and endometrial cancer, BRAFV600 mutations in melanoma, monoallelic BRCA1/2 mutations in ovarian cancer, and IDH mutations in glioblastoma, were reportedly always or usually utilized. The gene discussed is ESR1; the disease is glioblastoma.