Final answer:
Scientists identify oncogenes by studying genetic changes that cause normal cells to become cancerous, leading to discoveries such as the overexpression of HER2 in breast cancer, which was targeted with Herceptin. They also explore the functioning of mutant tumor suppressors and signaling pathways involved in cancer development.
Step-by-step explanation:
Scientists have historically identified oncogenes by exploring the genetic changes that transform normal cells into cancer cells. These genetic changes can occur at various levels, ranging from the gain or loss of entire chromosomes to mutations affecting single DNA nucleotides. There are two broad categories of genes affected by these changes: oncogenes and tumor suppressor genes. Oncogenes, such as HER2, are normal genes that are expressed at inappropriately high levels or altered genes with new functions, both lead to cancer cell proliferation.
Protein such as HER2, which is a cell-surface receptor, can be present in excessive amounts in some human breast cancers due to gene duplication leading to its overexpression. This was targeted by the development of a monoclonal antibody drug called Herceptin (trastuzumab), which assists the immune system in targeting HER2 for removal, contributing to increased overall survival in patients with metastatic breast cancer.
Furthermore, cancer biologists study mutant tumor suppressors and other molecular mechanisms involved in the onset of cancer. They do this by looking at growth factors, protein kinases, GTPases, transcription factors, and signaling pathways controlled by these genes. When mutations occur in genes such as RAS, they can result in uncontrolled cellular growth, leading to cancer.