Short answers, pulled from the story.
Cancer is a group of diseases involving uncontrolled cell growth that typically forms tumors able to invade or spread to other parts of the body. It develops when genes that regulate cell growth, such as oncogenes and tumor suppressor genes, are altered, and usually many genetic changes are required before cancer forms. Over 100 types of cancer affect humans.
Some 90 to 95% of cancers are due to environmental and lifestyle factors, while 5 to 10% are due to inherited genetics. Major contributors to cancer death include tobacco at 25 to 30%, diet and obesity at 30 to 35%, and infections at 15 to 20%. Around 40% of cancer can be prevented by avoiding or eliminating risk factors.
The word cancer comes from the ancient Greek karkinos, meaning crab and tumor. Greek physicians Hippocrates and Galen noted the resemblance of crabs to solid tumors with swollen veins fanning out from them. The word entered English in its modern medical sense around 1600.
A definitive cancer diagnosis requires a pathologist to examine a tissue sample from a biopsy, often after blood tests, X-rays, contrast CT scans, or endoscopy. The main treatments are surgery, chemotherapy, radiation therapy, hormonal therapy, targeted therapy, and palliative care. Newer immunotherapy approaches, in use since 1997, stimulate the immune system to fight cancer.
Survival depends on the cancer type and the stage at diagnosis. The average five-year survival rate in the United States is 66% for all ages, while children under 15 in the developed world average 80%. About half of patients treated for invasive cancer die from the disease or its treatment, and prognosis worsens once cancer has metastasized.
In 2018 there were 18.1 million new cancer cases and 9.6 million deaths globally, making cancer responsible for almost one in six deaths. As of 2020 the deadliest forms were lung cancer at 1.8 million deaths, colorectal at 916,000, liver at 830,000, stomach at 769,000, and breast at 685,000. The total economic cost of cancer has been estimated at US$1.16 trillion per year.
Approximately 18% of cancer deaths worldwide are related to infectious diseases, ranging from 25% in Africa to under 10% in the developed world. In 2018, infection caused 2.2 million cases, led by Helicobacter pylori at 810,000, human papillomavirus at 690,000, hepatitis B at 360,000, and hepatitis C at 160,000. All four can be vaccinated against or treated.