2016 BASIC CANCER FACTS
by The American Cancer Society
What Is Cancer?
Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. If the spread is not controlled, it can result in death. Cancer is caused by external factors, such as tobacco, infectious organisms, and an unhealthy diet, and internal factors, such as inherited genetic mutations, hormones, and immune conditions. These factors may act together or in sequence to cause cancer. Ten or more years often pass between exposure to external factors and detectable cancer. Treatments include surgery, radiation, chemotherapy, hormone therapy, immune therapy, and targeted therapy (drugs that interfere specifically with cancer cell growth).
Can Cancer Be Prevented?
A substantial proportion of cancers could be prevented. All cancers caused by tobacco use and heavy alcohol consumption could be prevented completely.
Certain cancers are related to infectious agents, such as human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), and Helicobacter pylori (H. pylori).
Many of these cancers could be avoided by preventing these infections through behavioral changes or vaccination, or by treating the infection. Many of the more than 5 million skin cancer cases that are diagnosed annually could be prevented by protecting skin from excessive sun exposure and not using indoor tanning devices. Screening can prevent colorectal and cervical cancers by allowing for the detection and removal of precancerous lesions.
Screening also offers the opportunity to detect some cancers early, when treatment is less extensive and more likely to be successful. Screening is known to help reduce mortality for cancers of the breast, colon, rectum, cervix, and lung (among long-term and/or heavy smokers). In addition, a heightened awareness of changes in certain parts of the body, such as the breast, skin, mouth, eyes, or genitalia, may also result in the early detection of cancer.
How Much Progress Has Been Made in the Fight against Cancer?
Trends in cancer death rates are the best measure of progress against cancer. The total cancer death rate rose for most of the 20th century because
of the tobacco epidemic, peaking in 1991 at 215 cancer deaths per 100,000 persons. However, from 1991 to 2012, the rate dropped 23% because of reductions in smoking, as well as improvements in early detection and treatment. This decline translates into the avoidance of more than 1.7 million cancer deaths. Death rates are declining for all four of the most common cancer types – lung, colorectal, breast, and prostate.
Who Is at Risk of Developing Cancer?
Cancer usually develops in older people; 86% of all cancers are diagnosed in people 50 years of age or older.
Certain behaviors also increase risk, such as smoking, eating an unhealthy diet, or not being physically active. Cancer researchers use the word “risk” in different ways, most commonly expressing risk as lifetime risk or relative risk. Lifetime risk refers to the probability that an individual will develop or die from cancer over the course of a lifetime.
These probabilities are estimated based on the overall experience of the general population and may overestimate or underestimate individual risk because of differences in exposures (e.g., smoking), family history, and/or genetic susceptibility.
Relative risk is a measure of the strength of the relationship between a risk factor and cancer. It compares the risk of developing cancer in people with a certain exposure or trait to the risk in people 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 of lung cancer is 25.
Most relative risks are not this large. For example, women who have a mother, sister, or daughter with a history of breast cancer are about twice as likely to develop breast cancer as women who do not have this family history; in other words, their relative risk is about 2. For most types of cancer, risk is higher with a family history of the disease. It is now thought that many familial cancers arise from the interplay between common gene variations and lifestyle/environmental risk factors. Only a small proportion of cancers are strongly hereditary, that is, caused by an inherited genetic alteration that confers a very high risk.
What Percentage of People Survive Cancer?
The 5-year relative survival rate for all cancers diagnosed during 2005-2011 was 69%, up from 49% during 1975-1977.
Improvement in survival reflects both the earlier diagnosis of certain cancers and improvements in treatment.
Survival statistics vary greatly by cancer type and stage at diagnosis. Relative survival is the percentage of people who are alive a designated time period (usually 5 years) after a cancer diagnosis divided by the percentage expected to be alive in the absence of cancer based on normal life expectancy.
It does not distinguish between patients who have no evidence of cancer and those who have relapsed or are still in treatment.
The 5-year relative survival rate does not represent the proportion of people who are cured because cancer deaths occur beyond 5 years after diagnosis.
How Is Cancer Staged?
Staging describes the extent or spread of cancer at the time of diagnosis. Proper staging is essential for optimizing therapy and assessing prognosis. A cancer’s stage is based on the size or extent of the primary tumor and whether it has spread to nearby lymph nodes or other areas of the body