Cancer Basics

What is cancer?

Cancer is a group of diseases characterized by uncontrolled growth and spread of abnormal cells. If the spread is not controlled, it can result in death. Although the reason for many cancers, particularly those that occur during childhood, remains unknown, established cancer causes include external factors such as tobacco, chemicals, radiation, and infectious organisms, and internal factors such as inherited mutations, hormones, immune conditions, and mutations that occur from metabolism. These casual factors may act together or in sequence to initiate or promote carcinogenesis. Ten or more years often pass between exposure to external factors and detectable cancer. Cancer is treated with surgery, radiation, chemotherapy, hormone therapy, biological therapy, and targeted therapy.

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Can cancer be prevented?

All cancers caused by cigarette smoking and the heavy use of alcohol could be prevented completely. The American Cancer Society estimates that in 2017 about 190,500 of the estimated 600,920 cancer deaths in the U.S. are expected to be caused by tobacco use.

The World Cancer Research Fund estimates that 20% of all cancers diagnosed in the U.S. are caused by a combination of excess body weight, physical inactivity, excess alcohol consumption, and poor nutrition, and thus could be prevented. In addition, many of the more than 5 million skin cancers that are expected to be diagnosed in 2017 could be prevented by protecting skin from excessive sun exposure and not using indoor tanning devices. Finally, certain cancers caused by infectious agents such as human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), and Helicobactor pylori (H. pylon) could be prevented through behavior changes, vaccination, or treatment of the infection.

Screening examinations conducted regularly by a health care professional can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, oral cavity, and skin at early stages. The screening-accessible cancers listed above account for approximately half of all new cancer cases. For most of these cancers, early detection has proven to reduce mortality. 

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Who is at risk of developing cancer?

Anyone can develop cancer. Since the risk of being diagnosed with cancer increases as individuals age, most cases occur in adults who are middle-aged or older. About 87% of all cancers are diagnosed in persons 50 and older. 

Lifetime risk refers to the probability that an individual, over the course of a lifetime, will develop or die from cancer. In the U.S., approximately 41 out of 100 men will develop cancer during their lifetime. For women, approximately 38 out of 100 will develop cancer during their lifetime.

Relative risk is a measure of the strength of the relationship between risk factors and a particular cancer. It compares the risk of developing cancer in persons with a certain exposure or trait to the risk in persons who do not have this characteristic. For example, men and women who smoke are about 25 times more likely to develop lung cancer than nonsmokers, so their relative risk is 25. Most relative risks are not this large. For example, women who have a first-degree relative (mother, sister, or daughter) with a history of breast cancer have about twice the risk of developing breast cancer compared with women who do not have a family history.

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How many people alive today have ever had cancer?

The National Cancer Institute estimates that approximately 15.5 million Americans with a history of cancer were alive in January 2016. Some of these individuals were cancer-free, while others still had evidence of cancer and may have been undergoing treatment.

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How many new cases are expected to occur this year?

About 1,688,780 new cancer cases are expected to be diagnosed in 2017. This estimate does not include carcinoma in situ (noninvasive cancer) of any site except urinary bladder, and does not include basal and squamous cell skin cancers. More than 5 million cases of basal and squamous cells skin cancer are expected to be diagnosed this year.

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How many people are expected to die of cancer?

In 2017, about 600,920 Americans are expected to die of cancer, approximately 1,650 people a day. Cancer is the second most common cause of death in the U.S., exceeded only by heart disease. In the US, cancer accounts for nearly 1 of every 4 deaths.

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What are the costs of cancer?

The Agency for Healthcare Research and Quality estimates that the direct medical costs (total of all health care expenditures) for cancer in the U.S. in 2014 were $87.8 billion.

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Page last updated: November 15, 2019