What is Cancer?

Cancer is not a single disease, but a process where the body’s normal systems of cell activity control break down. Normally, your DNA, tumor suppressor genes, repair systems, and immune defenses work together to regulate cell growth, fix mistakes, and destroy cells that don’t belong. Cancer begins when enough of these safeguards fail. The result is that abnormal cells start dividing uncontrollably, avoid being destroyed, and eventually form tumors and may spread to other parts of the body.

Breakdowns that are required for any cancer to survive and grow (any or all):

• Genetic mutations in key genes (tumor suppressors or oncogenes)
• Failure of tumor suppressors (like TP53 or BRCA)
• DNA repair breakdown (so errors accumulate)
• Avoidance of apoptosis (damaged cells refuse to die)
• Immune evasion (at least partly — though some cancers are more “invisible” than others)

Not all cancers use every mechanism to the same extent:

• Oncogene activation → Common in many cancers, but which oncogenes are active (e.g., KRAS, HER2) depends on the cancer type.
• Angiogenesis (blood vessel growth) → Critical for solid tumors (breast, lung, colon, sarcoma), but less relevant in blood cancers like leukemia.
• Metastasis → Not all cancers metastasize. Some stay localized for years or forever, but some can metastasize which means they move to other parts of the body.
• Hormone dependence → Some cancers (breast, prostate, endometrial) are fueled by hormones, but this isn’t universal.