Cancer cells have historically been classified by microscopic analysis of blood smears and tissue sections. Current technologies use molecular techniques to categorize and classify tumor cells by the identification of chromosomal aberrations, and the increased or decreased expression of genes and gene products. Both genomics (the study of genes) and proteomics (the study of proteins) are therefore essential components of molecular diagnostics, which determines how genes and proteins interact in a cell. The molecular signature or profile of a cancer cell can be determined by the presence or absence of gene activity in cancer and pre-cancerous cells by real time PCR, fluorescence in situ hybridization, microarrays, etc. This profile allows for enhanced detection, earlier and more accurate diagnosis and prognosis, and can aid the physician in determining if cancer cells persist after treatment, all of which, are factors that contribute to the highest quality in patient care. Objectives: 1. Contrast oncogenes with tumor-suppressor genes and list three of each 2. Explain loss of heterozygosity and a common mechanism of its detection 3. Describe FISH and its application in one type of cancer