Cells that stop following the rules
Our bodies constantly make new cells to replace old or damaged ones. Cancer begins when changes in a cell's DNA cause it to grow and divide without the usual controls.
Science · Educational overview
Understanding cancer, one layer at a time.
A plain-language introduction to how cancer develops, how it is tested and the main types of treatment — so the terms in your reports and conversations feel less unfamiliar.
Educational only.
This page provides general information and is not medical advice. Every cancer and every person is different —
please discuss your own situation with your treating team.
Cancer basics
What is cancer?
Many diseases, not one
Cancers are named by where they start (for example, lung or breast), but tumours from the same organ can behave very differently depending on their cell type and molecular changes.
Why context matters
Stage, grade, histology, biomarkers, previous treatment and overall health all shape which options are appropriate. The same test result can mean different things in different people.
The hallmarks of cancer
The shared capabilities cancers acquire
Researchers Douglas Hanahan and Robert Weinberg described a set of 'hallmarks' — capabilities that most cancers acquire as they develop. The framework was first published in 2000 and updated in 2011 and 2022.
- Sustaining proliferative signalling Keeping “grow” signals switched on.
- Evading growth suppressors Ignoring the brakes that normally stop cell division.
- Resisting cell death Avoiding the programmed self-destruction of damaged cells.
- Enabling replicative immortality Dividing far more times than normal cells can.
- Inducing or accessing vasculature Building or co-opting blood supply to feed the tumour.
- Activating invasion & metastasis Spreading into nearby tissue and to distant organs.
- Reprogramming cellular metabolism Changing how cells use energy and nutrients.
- Avoiding immune destruction Hiding from, or switching off, the immune response.
- Genome instability & mutation An enabling characteristic that speeds up genetic change.
- Tumour-promoting inflammation An enabling characteristic where inflammation fuels growth.
- Unlocking phenotypic plasticity Cells changing identity to escape normal maturation (2022).
- Non-mutational epigenetic reprogramming Gene activity changing without DNA mutations (2022).
- Polymorphic microbiomes Microbes in and around the body influencing cancer (2022).
- Senescent cells Ageing cells releasing signals that may support tumours (2022).
The 2022 update presented phenotypic plasticity and senescent cells as emerging hallmarks, and epigenetic reprogramming and microbiomes as enabling characteristics.
Testing
Genomic testing vs biomarker testing
The two terms are often used interchangeably, but they are not quite the same.
Biomarker testing
A biomarker is any measurable sign in the body or tumour that gives information about the cancer. Biomarker tests can look at proteins (for example, by immunohistochemistry), genes, or other molecules.
Results may help describe the cancer, estimate how it might behave, or indicate whether certain treatments are more likely to help.
Genomic (molecular) testing
Genomic tests, such as next-generation sequencing (NGS) panels, read the DNA or RNA of tumour cells to find changes like mutations, fusions or copy-number changes. They can be done on tissue or, sometimes, blood (“liquid biopsy”).
Genomic tests are one kind of biomarker test. Separately, germline (inherited) testing looks at DNA you were born with and can matter for you and your family.
Treatment categories
The main types of cancer treatment
Most people receive a combination. Which options are suitable depends on the cancer type, stage, biomarkers and personal circumstances.
Surgery
Removing the tumour and sometimes nearby lymph nodes. Often used when cancer is found early and is localised.
Radiotherapy
High-energy radiation aimed at the tumour to damage cancer cells, given from outside the body or internally.
Chemotherapy
Medicines that kill rapidly dividing cells, given as tablets or into a vein, often in cycles.
Targeted therapy
Medicines designed to act on specific molecular changes in cancer cells — which is why biomarker testing matters.
Immunotherapy
Treatments that help the immune system recognise and attack cancer, such as immune checkpoint inhibitors.
Hormone therapy
Blocking or lowering hormones that some cancers (such as many breast and prostate cancers) use to grow.
ADCs & radioligands
Antibody–drug conjugates and radioligand therapies deliver a toxic or radioactive payload to cells carrying a specific target.
Clinical trials
Research studies testing new treatments or combinations. They can offer access to new options under careful monitoring.
Sources
Where to read more
General references used to prepare this educational overview.
- Hanahan D, Weinberg RA. The hallmarks of cancer. Cell. 2000;100(1):57–70.
- Hanahan D, Weinberg RA. Hallmarks of cancer: the next generation. Cell. 2011;144(5):646–674.
- Hanahan D. Hallmarks of cancer: new dimensions. Cancer Discovery. 2022;12(1):31–46.
- National Cancer Institute (NCI) — cancer.gov: About Cancer (opens in a new tab), including information on biomarker testing and types of treatment.
- European Society for Medical Oncology (ESMO) — ESMO Patient Guides (opens in a new tab).
- National Comprehensive Cancer Network (NCCN) — NCCN Guidelines for Patients (opens in a new tab).
Want to know how we weigh evidence? Read about our evidence approach.