KRAS Mutation Explained: G12C, G12D, G12V and Treatment Options

KRAS (Kirsten rat sarcoma viral oncogene homolog) encodes a small protein that acts as a molecular switch inside the RAS/MAPK signalling pathway, one of the main relay systems that tells a cell when to grow and divide. Normally, KRAS cycles between an "on" state (bound to a molecule called GTP) and an "off" state (bound to GDP), turning growth signals on only briefly when needed.

A KRAS mutation changes a single amino acid in the protein, most often at position 12, and traps the switch in the "on" position. The cell then receives a continuous growth signal regardless of what is happening outside it, which is a hallmark of cancer. This is why KRAS is described as an oncogene: a mutated, activated version of a normal gene that promotes tumour formation.

The most frequent KRAS variants are named for the exact amino-acid substitution. G12C replaces glycine with cysteine at position 12; G12D replaces it with aspartate; G12V replaces it with valine. Other, less common variants include G12A, G12S, G13D and Q61 mutations. Each variant has a slightly different structure, which matters enormously for drug design: the G12C mutation creates a unique pocket that specific inhibitor drugs can bind to, while G12D and G12V do not have that same pocket and have required different chemical strategies to target, which is why the drug pipeline for these variants developed later.

If your report shows a KRAS mutation, three things are worth clarifying with your oncologist: which cancer type you have, which exact variant was found (G12C, G12D, G12V, or another), and whether that variant currently has an approved or trial-available targeted therapy in your situation. The clinical meaning of "KRAS-mutant" differs substantially between a colorectal cancer, where it usually rules out anti-EGFR treatment, and a lung cancer with a G12C mutation, where it can open the door to an oral targeted drug.

A KRAS mutation found in tumour tissue is a somatic change — it developed in the cancer cells during the person's lifetime and is not passed on to children, so it does not require genetic counselling for relatives in the way an inherited mutation such as BRCA1 or BRCA2 would. It is also worth knowing that a KRAS mutation can coexist with other alterations, so a comprehensive biomarker panel, part of the broader field of cancer biomarkers testing, is usually more informative than a single-gene test.

KRAS testing does not diagnose cancer itself; it is performed after a cancer diagnosis has been established by biopsy and pathology review, as part of the molecular workup that guides treatment selection. In colorectal cancer, RAS testing (KRAS and NRAS together) is considered a required step before anti-EGFR therapy is considered for metastatic disease. In NSCLC, KRAS is typically included in broad molecular panels alongside EGFR, ALK, ROS1 and other actionable genes at the time of advanced-stage diagnosis, since guidelines recommend comprehensive testing rather than single-gene assays whenever feasible. In pancreatic cancer, KRAS mutations are so common that some laboratories test for them as part of routine confirmation of diagnosis, alongside broader panels looking for the smaller subset of patients with other actionable alterations.

KRAS testing is most often performed on tumour tissue obtained from a biopsy or surgical specimen, using next-generation sequencing (NGS) panels that read many genes simultaneously, or targeted PCR-based assays that check specifically for the most common hotspot mutations. NGS has the advantage of identifying the exact variant (G12C versus G12D versus G12V, for example) along with any co-occurring alterations, which increasingly guides treatment choice and trial eligibility.

When tissue is limited, difficult to obtain safely, or when doctors want to track how a tumour is changing over time, a liquid biopsy can be used instead. This blood-based test detects circulating tumour DNA (ctDNA) shed by cancer cells and can identify KRAS mutations without a new procedure. Liquid biopsy is also increasingly used to monitor for emerging resistance mutations after treatment with a targeted KRAS inhibitor, since repeat tissue biopsies are not always practical.

Results typically take one to three weeks and are reported alongside other actionable findings in a molecular pathology report. Because KRAS mutation status directly affects whether certain drugs should or should not be used, testing is recommended at diagnosis for metastatic colorectal cancer and NSCLC, and may be repeated if the disease progresses or a new treatment decision point is reached.

KRAS mutations occur across many solid tumours but are especially prominent in three: pancreatic, colorectal and lung cancer.

Pancreatic cancer has one of the highest KRAS mutation rates of any tumour type, with mutations found in roughly 90% of pancreatic ductal adenocarcinomas. G12D and G12V are the dominant variants here, while G12C is comparatively rare. Because KRAS mutation is so nearly universal in this cancer, it has historically served more as a diagnostic and biological marker than a direct treatment target, although newer G12D-directed and pan-KRAS approaches are now entering trials specifically for pancreatic cancer.

Colorectal cancer carries KRAS mutations in roughly 30–50% of cases, with G12D and G12V again the most frequent variants and G12C present in a smaller subset. In this cancer, KRAS status is tested primarily to guide the use of anti-EGFR antibodies: any RAS mutation predicts a lack of benefit from cetuximab or panitumumab, so these drugs are reserved for RAS wild-type tumours. G12C-directed inhibitors, often combined with an anti-EGFR antibody, are being studied specifically in KRAS G12C-mutant colorectal cancer.

Non-small cell lung cancer (NSCLC) has KRAS mutations in roughly a quarter of cases, and here G12C is the most common variant, found more often in patients with a smoking history than other lung cancer driver mutations such as EGFR. This is the cancer type where KRAS G12C inhibitors were first approved, generally for patients who have already received at least one prior line of systemic therapy.

KRAS mutations also occur, less frequently, in cancers of the biliary tract, endometrium, and other sites, and are being studied wherever they appear.

For KRAS G12C-mutant NSCLC, approved oral KRAS G12C inhibitors are available for patients who have progressed on at least one prior systemic therapy, and trials are testing these drugs earlier in treatment and in combination with immunotherapy or chemotherapy. For KRAS G12C-mutant colorectal cancer, combinations of a KRAS G12C inhibitor with an anti-EGFR antibody are being studied and, in some settings, used, based on the idea that blocking the pathway at two points can overcome the resistance that limits single-agent activity in this cancer.

For the G12D and G12V variants, which are the most common in pancreatic and colorectal cancer, a new generation of inhibitors and "pan-KRAS" or "pan-RAS" drugs designed to hit multiple variants at once are in active clinical development, and enrolling in a clinical trial is often the most direct way to access these agents. Beyond mutation-specific drugs, KRAS-mutant tumours are also being studied with strategies that target proteins downstream or alongside the RAS pathway, including SHP2 inhibitors and combinations with MEK inhibitors, aiming to delay or overcome resistance.

When no KRAS-targeted option applies, standard treatments — chemotherapy, radiotherapy, surgery, anti-angiogenic therapy and immunotherapy where indicated — remain effective and appropriate, and a KRAS-mutant result does not mean these options are less suitable.