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?

A substantial proportion of cancers could be prevented, including all cancers caused by tobacco use and other unhealthy behaviors. According to a recent study by American Cancer Society researchers, at least 42% of newly diagnosed cancers in the US – about 750,000 cases in 2020 – are potentially avoidable, including the 19% of all cancers that are caused by smoking and the 18% caused by a combination of excess body weight, alcohol consumption, poor nutrition, and physical inactivity.

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 can help prevent colorectal and cervical cancers by detecting precancerous lesions that can be removed. It can also detect some cancers early, when treatment is more often successful. Screening is known to reduce mortality for cancers of the breast, colon, rectum, cervix, lung (among current or former heavy smokers), and probably prostate. In addition, being aware of changes in the body, such as the breast, skin, mouth, eyes, or genitalia, and bringing these to the attention of a health care professional, may also result in the early detection of cancer.

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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 80% of all cancers are diagnosed in persons 55 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 40 out of 100 men will develop cancer during their lifetime. For women, approximately 39 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 more than 16.9 million Americans with a history of cancer were alive on January 1, 2019, most of whom were diagnosed many years ago and have no current evidence of cancer.

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How many new cases are expected to occur this year?

More than 1.8 million new cancer cases are expected to be diagnosed in 2020. This estimate does not include carcinoma in situ (noninvasive cancer) of any site except urinary bladder; nor does it include basal cell or squamous cell skin cancers because these types of skin cancer are not required to be reported to cancer registries. 28,570 of those cases will occur in Alabama.

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How many people are expected to die of cancer?

About 606,520 Americans are expected to die of cancer in 2020, which translates to about 1,660 deaths per day. Cancer is the second most common cause of death in the US, exceeded only by heart disease. American Cancer Society estimates 10,530 will die from various types of cancer in Alabama.

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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 US in 2015 were $80.2 billion with 52% of those costs resulting from hospital outpatient or office-based provider visits and 38% from inpatient hospital stays. In addition to these costs, researchers at the American Cancer Society recently estimated that more than $94 billion in earnings were lost in the US in 2015 due to cancer death.

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Page last updated: July 14, 2020