Cancer-Causing Genes: Oncogenes vs. Tumor Suppressors Explained

Cancer arises from mutations in two broad gene classes that normally regulate cell growth:

Oncogenes: Accelerators of Growth

• Mutated/overactive versions of proto-oncogenes (normal growth promoters).
• Gain-of-function mutations: excessive signaling for proliferation.
• Examples: HER2 (breast), RAS (pancreatic, colon), MYC (lymphoma), BCR-ABL (CML).
• Analogy: Stuck accelerator pedal.

Tumor Suppressor Genes: Failed Brakes

• Normal function: inhibit proliferation, promote DNA repair, trigger apoptosis.
• Loss-of-function mutations: both alleles typically inactivated (Knudson's two-hit hypothesis).
• Examples: TP53 (most cancers), RB1 (retinoblastoma), PTEN, APC (colon), BRCA1/2 (breast/ovarian).
• Analogy: Cut brake lines.

Clinical Relevance

Targeted therapies often inhibit oncogenic drivers (e.g., trastuzumab for HER2+, imatinib for BCR-ABL). Tumor suppressor loss is harder to target directly but informs prognosis and PARP inhibitor use in BRCA-mutated cancers.