Tumor Suppressor Genes Explained

Tumor suppressor genes encode proteins that restrain cell proliferation, trigger DNA repair, or initiate apoptosis when cellular stress exceeds safe thresholds. Unlike oncogenes, they typically require both copies to be inactivated — Knudson's two-hit hypothesis — before their protective effect is eliminated. This explains why hereditary cancer syndromes caused by inherited tumor suppressor mutations (Li-Fraumeni, BRCA1, Lynch syndrome) cause earlier-onset and more aggressive disease: carriers begin life with one hit already present.

Quick Answer

Proteins that act as molecular brakes on cell division. Loss of both copies unlocks uncontrolled proliferation. This category links the major genes to their molecular mechanisms, cancer associations, and related pathway pages.

Key Genes in This Category

TP53

The most frequently mutated gene in human cancer, encoding p53 — a transcription factor that integrates DNA damage, oncogene activation, and metabolic stress to impose cell cycle arrest, DNA repair, or apoptosis. Lost in >50% of all cancers.

BRCA1

Essential coordinator of homologous recombination repair of DNA double-strand breaks. Germline mutations confer ~50–70% lifetime breast cancer and ~40–45% ovarian cancer risk; somatic loss is the basis for PARP inhibitor synthetic lethality.

PTEN

Lipid phosphatase opposing PI3K by dephosphorylating PIP3, making it the primary negative regulator of the AKT/mTOR survival axis. Deleted or mutated in ~30% of glioblastomas and prostate cancers; germline loss causes Cowden syndrome.

RB1

Encodes pRb, which enforces the G1/S restriction point by sequestering E2F transcription factors. Biallelic inactivation causes retinoblastoma and is near-universal in small cell lung cancer; virtually every cancer disrupts the pRb pathway.

ATM

Master kinase activated by DNA double-strand breaks, phosphorylating hundreds of substrates including p53, CHK2, and BRCA1 to coordinate repair and checkpoints. Germline mutations cause ataxia-telangiectasia; somatic loss is common in CLL.

CDKN2A

Encodes two separate tumor suppressors: p16INK4a (inhibits CDK4/CDK6) and p14ARF (stabilises p53 via MDM2 inhibition). Deleted in ~50% of melanomas and ~30% of glioblastomas, simultaneously disabling both the RB and p53 pathways.

MDM2

E3 ubiquitin ligase and primary negative regulator of p53; amplified in ~10% of liposarcomas, functionally inactivating p53 without TP53 mutation. MDM2 inhibitors are in clinical trials for MDM2-amplified, TP53-wild-type sarcomas.

VHL

E3 ubiquitin ligase component degrading HIF-1/2α under normoxia. Biallelic loss in clear cell renal carcinoma (~90%) causes constitutive HIF activation and VEGF-driven angiogenesis; targeted by belzutifan and anti-VEGF agents.

MLH1

DNA mismatch repair protein in the MutLα complex. Loss causes microsatellite instability (MSI-high), Lynch syndrome-associated colorectal and endometrial cancers, and high sensitivity to PD-1 immune checkpoint blockade.

CHEK2

CHK2 kinase activated by ATM after double-strand breaks, reinforcing p53 and BRCA1 activation. Germline CHEK2 variants moderately elevate breast and colorectal cancer risk; loss impairs DNA damage checkpoint fidelity.

Explore Other Categories

Oncogenes

Gain-of-function mutations in growth-promoting genes that drive continuous cell division, even without normal growth signals.

Apoptosis Regulators

Genes that determine whether a damaged or stressed cell lives or dies. Cancer hijacks these to evade programmed cell death.

DNA Repair Genes

Genes maintaining genome integrity through detection and correction of DNA damage. Their loss drives mutagenesis and cancer predisposition.

Cell Cycle Regulators

Proteins controlling when and how cells divide. Disruption of these checkpoints is nearly universal in human cancer.

Gene descriptions are based on peer-reviewed literature from PubMed, UniProt, and NCBI Gene. Information is for educational purposes only.