KRAS is a gene that provides the code for making a protein, KRAS, which is involved primarily in controlling cell division. This protein is part of the MAP kinase signaling cascade (RAS/RAF/MEK/ERK) that relays chemical signals from outside the cell to the cell's nucleus and is primarily involved in controlling cell division. KRAS is an enzyme (a GTPase) that converts a molecule called GTP into GDP. When KRAS is attached (bound) to GDP, it's in its "off" position and can't send signals to the nucleus. But when a GTP molecule arrives and binds to KRAS, KRAS is activated and sends its signal, and then it converts the GTP into GDP and returns to the "off" position.
When mutated, KRAS can act as an oncogene, causing normal cells to become cancerous. The mutations can shift the KRAS protein into the "on" position all the time. KRAS mutations are common in pancreatic, lung and colorectal cancers. These KRAS mutations are said to be somatic, because instead of coming from a parent and being present in every cell (hereditary), they are acquired during the course of a person's life and are found only in cells that become cancerous.
Tumor mutation profiling performed clinically at the MGH Cancer Center has identified KRAS mutations across a broad-spectrum of cancer types. The highest incidence of KRAS mutations have been found in pancreatic cancer (70%), colon cancer (30%), lung cancer (25%), cholangiocarcinoma (15-20%), acute myeloid leukemia (15-20%) and endometrial cancer (15-20%). Across the other major tumor types, KRAS mutations have been found in less than 10% of cases that have been tested.
KRAS (v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog) is a member of the closely related RAS gene family that includes NRAS and HRAS. These RAS members are small GTPases that transduce extracellular signals to the downstream effectors RAF, PI3K and RALGDS. Ras members are involved in regulating diverse cellular processes including survival, proliferation and differentiation. While activating mutations in the RAS genes lead to sustained GTPase activation and are tumorigenic, each oncogene exerts clear phenotypic differences. KRAS is the most frequently mutated gene from the RAS family, occurring in approximately 20% of all human cancers. Mutational hotspots in KRAS reside primarily in amino acid residues 12, 13 or 61 and function to promote hyperproliferation and suppress differentiation.
The KRAS G12C mutation arises from a single nucleotide change (c.34G>T) and results in an amino acid substitution of the glycine (G) at position 12 by a cysteine (C).
Genetic alterations in the gene encoding KRAS have been found in lung cancer. These mutations result in an altered protein, one that cannot be normally regulated. The mutated form of KRAS is constantly activated, sending growth and proliferation signals to tumor cells. The specific mutation G12C has therapeutic implications and may result in different treatment recommendations from an oncologist.
Testing for KRAS mutations, including G12C, can be performed in the MGH Center for Integrated Diagnostics. Treatments for KRAS mutant lung cancer are available at the MGH Cancer Center, and clinical trials testing new drugs and improved treatments are also available.