Named After a Crab
The name is a piece of ancient observation. The word comes from the ancient Greek *karkinos*, meaning both crab and tumour. Greek physicians including Hippocrates and Galen noted how closely some tumours, with their swollen surrounding veins, resembled a crab. The word entered English in its modern medical sense around 1600.
Cancer is not one disease. It is a group of diseases involving uncontrolled cell growth, typically producing tumours with the potential to invade or spread to other parts of the body. Over 100 types affect humans.
The key distinction is between malignant tumours, which can spread, and benign tumours, which do not. Both belong to the wider family of neoplasms, groups of cells that have undergone unregulated growth and often form a lump or mass.
The Six Things Every Cancer Cell Learns
All tumour cells display what are known as the six hallmarks of cancer. These characteristics are required to produce a malignant tumour, and reading them together explains why the disease is so hard to stop:
- Growing and dividing without the proper signals to do so
- Continuing to grow and divide even when signalled to stop
- Avoiding programmed cell death
- Dividing a limitless number of times
- Promoting the construction of new blood vessels to feed itself
- Invading tissue and forming metastases elsewhere in the body
The journey from normal cells, to a detectable mass, to cancer proper happens in multiple steps known as malignant progression. Typically many genetic changes are required before cancer develops at all, which is one reason risk rises significantly with age.
How Much of It Is Preventable
About 33% of deaths from cancer are caused by tobacco and alcohol, obesity, a diet lacking fruit and vegetables, and lack of exercise. Roughly a third of the toll traces to things that are, at a population level, modifiable.
Infections matter more than most people realise. Specific viruses, bacteria and parasites cause approximately 16 to 18% of cancers worldwide, including Helicobacter pylori, hepatitis B, hepatitis C and HPV. Vaccination against hepatitis B and human papillomavirus has been shown to nearly eliminate the risk of the cancers those viruses cause.
Only about 5 to 10% of cancers are due to inherited genetic defects. Other contributors include ionizing radiation and environmental pollutants. These environmental factors act, at least partly, by changing the genes inside a cell.
The Great Imitator
When cancer begins, it produces no symptoms at all. Signs appear only as a mass grows or ulcerates, and what shows up depends entirely on type and location. Few symptoms are specific to cancer, and many of them commonly occur in people with completely different conditions. For that reason it has been called a great imitator.
Detection therefore relies on signs, symptoms or screening tests, followed by medical imaging and confirmed by biopsy. Early detection through screening is useful for cervical and colorectal cancer. The benefits of breast cancer screening are debated.
Treatment usually combines radiation therapy, surgery, chemotherapy and targeted therapy. More personalised approaches that harness the patient's own immune system are emerging in the field of immunotherapy. Palliative care, a specialty delivering advanced pain and symptom management, matters especially in advanced disease.
The Global Picture, in Numbers
In 2015, about 90.5 million people worldwide were living with cancer. In 2019 there were 23.6 million new cases and 10 million deaths, increases of 26% and 21% respectively over the previous decade.
The common types split by sex. In males: lung, prostate, colorectal and stomach cancer. In females: breast, colorectal, lung and cervical cancer. If skin cancers other than melanoma were counted in the totals, they would make up around 40% of all new cases each year. In children, acute lymphoblastic leukemia and brain tumours are most common, except in Africa where non-Hodgkin lymphoma occurs more often.
Survival depends heavily on the type and on how far the disease has progressed at the start of treatment. For children under 15 at diagnosis, the five-year survival rate in the developed world averages 80%. Across all ages in the United States, the average five-year survival rate is 66%.
