Cancer
Understanding Cancer
A foundational overview of cancer as a group of diseases and the vocabulary used in cancer statistics.
Beginner explanation
Cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body. It can start almost anywhere. Normally, cells grow and divide only when the body needs new ones, and old or damaged cells die. In cancer, that orderly process breaks down.[1]
Cancer is really a large group of diseases: there are more than 100 types, usually named for the organ or tissue where they start — lung cancer starts in the lung, for example.[1]
Cancer is a genetic disease, meaning it is caused by changes to genes that control how cells grow and divide. These changes can come from errors during cell division, from damage to DNA by harmful exposures such as tobacco smoke or ultraviolet light, or from genes inherited from parents.[1]
Key definitions
- Tumor
- A lump of tissue formed by abnormal cells. Tumors can be cancerous (malignant) or not cancerous (benign).
- Benign tumor
- A tumor that does not invade nearby tissue. Benign tumors can still be large or, in places like the brain, serious.
- Metastasis
- The spread of cancer cells from where they first formed to other parts of the body. Breast cancer that spreads to the lung is still breast cancer.
- Carcinoma in situ
- Abnormal cells that have not invaded nearby tissue. Sometimes called stage 0; usually treated because it may become cancer.
- Risk factor
- Anything that raises the chance of developing a disease. A risk factor does not mean a person will get cancer.
Condition characteristics
NCI describes several ways cancer cells differ from normal cells. Cancer cells can:[1]
- Grow without the signals that normally tell cells to grow
- Ignore signals that tell cells to stop dividing or to die
- Invade nearby tissue and spread to other parts of the body
- Signal blood vessels to grow toward tumors
- Hide from, or even exploit, the immune system
Source[1]
Many cancers form solid tumors, but blood cancers such as leukemias generally do not. Most people who die of cancer die of metastatic disease.[1]
Risk factors
It is usually not possible to know exactly why one person develops cancer and another does not. Research has identified factors that raise risk; some can be avoided and some, like growing older, cannot.[2]
NCI lists the most-studied known or suspected risk factors as:[2]
- Age
- Alcohol
- Cancer-causing substances
- Chronic inflammation
- Diet
- Hormones
- Immunosuppression
- Infectious agents
- Obesity
- Radiation
- Sunlight
- Tobacco
Source[2]
The body normally removes cells with damaged DNA, but this ability declines with age — part of the reason cancer risk is higher later in life.[1]
Prevention and public health context
Limiting exposure to avoidable risk factors, such as tobacco, may lower the risk of developing certain cancers.[2]
Statistics describe cancer in large groups of people — how many are diagnosed, how many die, and how many are living after diagnosis. They help governments, health professionals and researchers plan and measure efforts against cancer, but they are usually not directly applicable to an individual patient.[3]
NCI reports that the overall U.S. cancer death rate has declined since the early 1990s, while the number of cancer survivors has grown.[3]
Texas data context
The only cancer measure currently on MedEquity’s map is the PLACES cancer measure: the share of adults who report ever being told by a health professional that they had melanoma or another cancer, excluding non-melanoma skin cancer. This describes people living after a cancer diagnosis — not how many new cancers occur or how many people die.[4]
County cancer incidence for Texas (2019–2023, all sites and four common types) is on the Explore map, from Texas Cancer Registry data published by NCI and CDC on State Cancer Profiles. Counties with fewer than 16 cases are suppressed. County cancer death rates are not shown yet.
Related measures on the Explore map
- Cancer history (non-skin cancer or melanoma) among adults (modeled estimate)
Advanced material (optional)
Changes in cancer-causing genes tend to affect three main kinds of genes: proto-oncogenes (which can become cancer-driving oncogenes), tumor suppressor genes and DNA repair genes. Each person’s cancer has its own combination of genetic changes, and some treatments target specific changes regardless of where the cancer started.[1]
Not every tissue change is cancer. Hyperplasia (extra but normal-looking cells) and dysplasia (abnormal-looking cells) may or may not progress, which is why some changes are monitored rather than treated.[1]
References
- What Is Cancer?. National Cancer Institute (NIH). https://www.cancer.gov/about-cancer/understanding/what-is-cancer (accessed 2026-10-18).
- Risk Factors for Cancer. National Cancer Institute (NIH). https://www.cancer.gov/about-cancer/causes-prevention/risk (accessed 2026-10-18).
- Cancer Statistics. National Cancer Institute (NIH). https://www.cancer.gov/about-cancer/understanding/statistics (accessed 2026-10-18).
- PLACES Measure Definitions: Health Outcomes. Centers for Disease Control and Prevention. https://www.cdc.gov/places/measure-definitions/health-outcomes.html (accessed 2026-10-18).