In the field of oncology, clinical molecular diagnostics and biomarker discoveries are constantly advancing as the intricate molecular mechanisms that transform a normal cell into an aberrant state in concert with the dysregulation of alternative complementary pathways are increasingly understood. Progress in biomarker technology, coupled with the companion clinical diagnostic laboratory tests, continue to advance this field, where individualized and customized treatment appropriate for each individual patient define the standard of care. Here, we discuss the current commonly used predictive pharmacogenetic biomarkers in clinical oncology molecular testing: BRAF V600E for vemurafenib in melanoma; EML4-ALK for crizotinib and EGFR for erlotinib and gefitinib in non-small-cell lung cancer; KRAS against the use of cetuximab and panitumumab in colorectal cancer; ERBB2 (HER2/neu) for trastuzumab in breast cancer; BCR-ABL for tyrosine kinase inhibitors in chronic myeloid leukemia; and PML/RARα for all-trans-retinoic acid and arsenic trioxide treatment for acute promyelocytic leukemia.