KRAS vs NRAS vs HRAS: Three RAS Genes, Different Cancers

Same Switch, Different Tails

All three RAS proteins cycle between an active GTP-bound and an inactive GDP-bound state, relaying signals from receptors to the RAF-MEK-ERK and PI3K pathways. Their first 165 amino acids are nearly identical.

They diverge in the C-terminal hypervariable region, which controls how and where each protein attaches to membranes. This routes the isoforms to somewhat different membrane microdomains and downstream outputs.

KRAS

KRAS is the most frequently mutated RAS gene overall. It dominates in pancreatic (around 90 percent), colorectal (around 40 percent) and lung adenocarcinoma (around 30 percent), with codon 12 the main hotspot.

KRAS G12C is now directly druggable with covalent inhibitors (sotorasib, adagrasib) in lung cancer, and G12D-directed agents are in trials.

NRAS

NRAS mutations are most prominent in cutaneous melanoma (around 15 to 20 percent) and in a subset of acute myeloid leukaemia and other haematological cancers, with codon 61 a common site alongside codon 12.

NRAS-mutant melanoma is associated with aggressive behaviour, and MEK inhibition has modest single-agent activity; combination strategies are under study.

HRAS

HRAS mutations are comparatively rare but characteristic of specific cancers: head and neck squamous cell carcinoma, salivary gland tumours, bladder cancer and thyroid cancer. Germline HRAS variants cause Costello syndrome, a RASopathy.

The farnesyltransferase inhibitor tipifarnib exploits the fact that HRAS, unlike KRAS and NRAS, depends on farnesylation alone for membrane attachment, and has shown activity in HRAS-mutant head and neck cancer.

Interpretation Notes

Testing panels usually cover all three genes, but a result should specify which gene and which codon, since treatment relevance is isoform- and variant-specific.

In colorectal cancer, activating mutations in KRAS or NRAS (extended RAS testing) both predict lack of benefit from anti-EGFR antibodies; this is one context where the isoforms are grouped for a specific purpose.

Key Takeaways

• ·KRAS, NRAS and HRAS share a near-identical core but differ in membrane anchoring.
• ·KRAS dominates pancreatic, colorectal and lung cancer; NRAS in melanoma and some leukaemias; HRAS in head and neck, bladder and salivary tumours.
• ·Druggability differs: KRAS G12C inhibitors, MEK strategies for NRAS, tipifarnib for HRAS.
• ·Extended RAS testing in colorectal cancer groups KRAS and NRAS to predict anti-EGFR resistance.