Which of the following is a common oncogene?

K-ras (KRAS) is recognized as a common oncogene, primarily associated with various types of cancer, particularly pancreatic, colorectal, and lung cancers. Oncogenes are mutated or overexpressed versions of normal genes (proto-oncogenes) that promote cell growth and division. The K-ras gene encodes a protein that functions as a molecular switch in signaling pathways that control cell proliferation, differentiation, and survival.

When K-ras is mutated, it can lead to continuous activation of these signaling pathways, contributing to uncontrolled cell division and tumorigenesis. In nearly 30% of all human cancers, mutations in K-ras are present, making it an essential target for cancer research and therapy.

In contrast, the other options listed are generally classified as tumor suppressor genes or DNA repair genes rather than oncogenes. For instance, BRCA1 is involved in DNA repair and, when defective, is linked to breast and ovarian cancers. TP53 is known as the "guardian of the genome," and mutations in this gene lead to loss of its tumor-suppressing functions. MLH1 plays a role in DNA mismatch repair, and mutations are associated with Lynch syndrome, increasing the risk of certain cancers. Thus,