Tumor Suppressor Genes Explained

Tumor suppressor genes encode proteins that restrain cell proliferation, support DNA repair, or initiate apoptosis when cellular stress exceeds safe thresholds. Many follow a two-hit pattern in which both functional copies are lost within a tumour cell, although mechanisms differ by gene. Inherited pathogenic variants can reduce the number of additional events needed for tumorigenesis and can increase cancer risk or shift age of onset; they do not guarantee cancer or imply that every associated cancer will be more aggressive.

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

Coordinator of homologous recombination repair of DNA double-strand breaks. NCI estimates that more than 60% of women with an inherited harmful BRCA1 change develop breast cancer and about 39–58% develop ovarian cancer; individual risk varies, and tumour-only findings are not automatically inherited.

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.

Pathways and evidence guides

Move from the gene list into a mechanism map or a focused interpretation guide.

Tumour suppressor network

See how p53, RB, PTEN and DNA-repair controls interact.

Tumour suppressor genes explained

Compare two-hit inactivation across major gene families.

TP53 mutations in cancer

Separate loss of function, dominant-negative effects and inherited risk.

TP53, RB1, CDKN2A and MDM2 compared

Compare the p53 and RB systems side by side.

DNA-damage response

Follow damage sensing, checkpoints and repair decisions.

Core sources

Authoritative overviews and peer-reviewed sources supporting this category summary.

1What Is Cancer?. National Cancer Institute, 2026. Source
2Mutation and cancer: statistical study of retinoblastoma. Proc Natl Acad Sci USA, 1971. Source
3BRCA Gene Changes: Cancer Risk and Genetic Testing. National Cancer Institute, 2024. Source

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.