12.5: Cancer
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What Is Cancer?
Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.
Figure \(\PageIndex{1}\). Cancerous Cells
When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors. Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor. Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening.
Key Cancer Terms
- Neoplasms : clusters of abnormal cells; aka “tumors.” When the neoplasms or tumors grow out and replace normal cells they are said to be “infiltrating” or “metastasizing” which means traveling to other parts of the body via the blood or lymph.
- Carcinoma : most common form; starts in the epithelium.
- Sarcoma: forms in connective tissue: bones, muscles, blood vessels.
- Leukemias: form in blood-forming tissues: bone marrow, lymph nodes, and the spleen.
- Lymphomas : form in the cells of the lymph system (the system that filters out impurities and/or infection).
- Conceptually, cancer is thought to develop via the turning on of genes called “ oncogenes ” or genes that have gone awry. The DNA in these cells replicates at an accelerated rate. “Tumor suppressor genes”, which are present in all of us, fail to stop these cells from dividing thereby allowing a tumor to form.
- A “ malignant ” tumor is a cancerous tumor, whereas a “benign” tumor is not cancerous and of no imminent danger to the body.
How Cancer Arises
Cancer is caused by changes to genes that control the way our cells function, especially how they grow and divide.
Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.
When Cancer Spreads
In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumors (metastatic tumors) in other parts of the body. The metastatic tumor is the same type of cancer as the primary tumor.
A cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.
Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer. For example, breast cancer that spreads to and forms a metastatic tumor in the lung is metastatic breast cancer, not lung cancer.
Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
Cancer Stages
Cancers are staged 1-3/4, depending on the cancer and the severity. When detected at stage 1, a person suffering from most types of cancer has about a 95% of surviving. The odds go down as you get to stage 3 or 4 (some cancers only have 3 stages, others 4). Doctors will often add an ‘A’ or ‘B’ to the staging as well, and this can relate to whether or not the cancer has invaded other tissues.
Tissue Changes That Are Not Cancer
Not every change in the body’s tissues is cancer. Some tissue changes may develop into cancer if they are not treated, however. Here are some examples of tissue changes that are not cancer but, in some cases, are monitored:
Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up, or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.
Dysplasia is a more serious condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form.
Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not.
Normal cells may become cancer cells. Before cancer cells form in tissues of the body, the cells go through abnormal changes called hyperplasia and dysplasia. In hyperplasia, there is an increase in the number of cells in an organ or tissue that appear normal under a microscope. In dysplasia, the cells look abnormal under a microscope but are not cancer. Hyperplasia and dysplasia may or may not become cancer.
Types of Cancer
There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain. Cancers also may be described by the type of cell that formed them, such as an epithelial cell or a squamous cell.
Common Cancer Types
This list of common cancer types includes cancers that are diagnosed with the greatest frequency in the United States, excluding non-melanoma skin cancers:
- Bladder Cancer: The most common type of bladder cancer is transitional cell carcinoma, also called urothelial carcinoma. Smoking is a major risk factor for bladder cancer. Bladder cancer is often diagnosed at an early stage.
- Breast Cancer : Breast cancer is the second most common cancer in women after skin cancer. Mammograms can detect breast cancer early, possibly before it has spread.
- Colon and Rectal Cancer: Colorectal cancer often begins as a growth called a polyp inside the colon or rectum. Finding and removing polyps can prevent colorectal cancer.
- Endometrial Cancer: Uterine cancers can be of two types: endometrial cancer (common) and uterine sarcoma (rare). Endometrial cancer can often be cured. Uterine sarcoma is often more aggressive and harder to treat.
- Kidney Cancer: Kidney cancer can develop in adults and children. The main types of kidney cancer are renal cell cancer, transitional cell cancer, and Wilms tumor. Certain inherited conditions increase the risk of kidney cancer.
- Leukemia: Leukemia is a broad term for cancers of the blood cells. The type of leukemia depends on the type of blood cell that becomes cancer and whether it grows quickly or slowly. Leukemia occurs most often in adults older than 55, but it is also the most common cancer in children younger than 15.
- Lung Cancer: Lung cancer includes two main types: non-small cell lung cancer and small cell lung cancer. Smoking causes most lung cancers, but nonsmokers can also develop lung cancer.
- Melanoma: Skin cancer is the most common type of cancer. The main types of skin cancer are squamous cell carcinoma, basal cell carcinoma, and melanoma. Melanoma is much less common than the other types but much more likely to invade nearby tissue and spread to other parts of the body. Most deaths from skin cancer are caused by melanoma.
- Non-Hodgkin Lymphoma: Lymphoma is a broad term for cancer that begins in cells of the lymph system. The two main types are Hodgkin lymphoma and nonHodgkin lymphoma (NHL). Hodgkin lymphoma can often be cured. The prognosis of NHL depends on the specific type.
- Pancreatic Cancer: Pancreatic cancer can develop from two kinds of cells in the pancreas: exocrine cells and neuroendocrine cells, such as islet cells. The exocrine type is more common and is usually found at an advanced stage. Pancreatic neuroendocrine tumors (islet cell tumors) are less common but have a better prognosis.
- Prostate Cancer: Prostate cancer is the most common cancer and the second leading cause of cancer death among men in the United States. Prostate cancer usually grows very slowly, and finding and treating it before symptoms occur may not improve men's health or help them live longer.
- Thyroid Cancer: Thyroid cancer can be of four main types, which vary in their aggressiveness. Anaplastic thyroid cancer is hard to cure with current treatments, whereas papillary (the most common), follicular, and medullary thyroid cancer can usually be cured.
Cancer incidence and mortality statistics reported by the American Cancer Society and other resources were used to create the list. To qualify as a common cancer for the list, the estimated annual incidence for 2016 had to be 40,000 cases or more.
The most common type of cancer on the list is breast cancer, with more than 249,000 new cases expected in the United States in 2016. The next most common cancers are lung cancer and prostate cancer.
Because colon and rectal cancers are often referred to as “colorectal cancers,” these two cancer types are combined for the list. For 2016, the estimated number of new cases of colon cancer and rectal cancer are 95,270 and 39,220, respectively, adding to a total of 134,490 new cases of colorectal cancer.
The following table gives the estimated numbers of new cases and deaths for each common cancer type:
Table \(\PageIndex{1}\). Cancer Types
| Cancer Type | Estimated New Cases | Estimated Deaths |
| Bladder | 76,960 | 16,390 |
| Breast (Female - Male) | 246,660 - 2,600 | 40,450 - 440 |
| Colon and Rectal (Combined) | 134,490 | 49,190 |
| Endometrial | 60,050 | 10,470 |
| Kidney (Renal Cell and Renal Pelvis) Cancer | 62,700 | 14,240 |
| Leukemia (All Types) | 60,140 | 24,400 |
| Lung (Including Bronchus) | 224,390 | 158,080 |
| Melanoma | 76,380 | 10,130 |
| Non-Hodgkin Lymphoma | 72,580 | 20,150 |
| Pancreatic | 53,070 | 41,780 |
| Prostate | 180,890 | 26,120 |
| Thyroid | 64,300 | 1,980 |
Risk Factors for Cancer
It is usually not possible to know exactly why one person develops cancer and another doesn’t. But research has shown that certain risk factors may increase a person’s chances of developing cancer. (There are also factors that are linked to a lower risk of cancer. These are called protective factors.)
Cancer risk factors include exposure to chemicals or other substances, as well as certain behaviors. They also include things people cannot control, like age and family history. A family history of certain cancers can be a sign of a possible inherited cancer syndrome.
Most cancer risk (and protective) factors are initially identified in epidemiology studies. In these studies, scientists look at large groups of people and compare those who develop cancer with those who don’t. These studies may show that the people who develop cancer are more or less likely to behave in certain ways or to be exposed to certain substances than those who do not develop cancer.
Such studies, on their own, cannot prove that a behavior or substance causes cancer. For example, the finding could be a result of chance, or the true risk factor could be something other than the suspected risk factor. But findings of this type sometimes get attention in the media, and this can lead to wrong ideas about how cancer starts and spreads.
When many studies all point to a similar association between a potential risk factor and an increased risk of cancer, and when a possible mechanism exists that could explain how the risk factor could actually cause cancer, scientists can be more confident about the relationship between the two.
The list below includes the most studied known or suspected risk factors for cancer:
- Age
- Alcohol
- Cancer-Causing Substances
- Chronic Inflammation
- Diet
- Hormones
- Immunosuppression
- Infectious Agents
- Obesity
- Radiation
- Sunlight
- Tobacco
Figure \(\PageIndex{2}\). CDC Advertisement
Although some of these risk factors can be avoided, others—such as growing older— cannot. Limiting your exposure to avoidable risk factors may lower your risk of developing certain cancers.
TOBACCO
Tobacco use is a leading cause of cancer and of death from cancer. People who use tobacco products or who are regularly around environmental tobacco smoke (also called secondhand smoke) have an increased risk of cancer because tobacco products and secondhand smoke have many chemicals that damage DNA.
Tobacco use causes many types of cancer, including cancer of the lung, larynx (voice box), mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon and rectum, and cervix, as well as acute myeloid leukemia. People who use smokeless tobacco (snuff or chewing tobacco) have increased risks of cancers of the mouth, esophagus, and pancreas.
There is no safe level of tobacco use. People who use any type of tobacco product are strongly urged to quit. People who quit smoking, regardless of their age, have substantial gains in life expectancy compared with those who continue to smoke. Also, quitting smoking at the time of a cancer diagnosis reduces the risk of death.
Scientists believe that cigarette smoking causes about 30% of all cancer deaths in the United States.
Cancer Prevention
The number of new cancer cases can be reduced and many cancer deaths can be prevented. Research shows that screening for cervical and colorectal cancers as recommended helps prevent these diseases by finding precancerous lesions so they can be treated before they become cancerous. Screening for cervical, colorectal, and breast cancers also helps find these diseases at an early stage, when treatment works best.
Vaccines (shots) also help lower cancer risk. The human papillomavirus (HPV) vaccine helps prevent most cervical cancers and several other kinds of cancer, and the hepatitis B vaccine can help lower liver cancer risk.
A person’s cancer risk can be reduced with healthy choices like avoiding tobacco, limiting alcohol use, protecting your skin from the sun and avoiding indoor tanning, eating a diet rich in fruits and vegetables, keeping a healthy weight, and being physically active.
Avoiding Tobacco
Cigarette Smoking
Lung cancer is the leading cause of cancer death, and cigarette smoking causes almost all cases. Compared to nonsmokers, current smokers are about 25 times more likely to die from lung cancer. Smoking causes about 80% to 90% of lung cancer deaths. Smoking also causes cancer of the mouth and throat, esophagus, stomach, colon, rectum, liver, pancreas, voicebox (larynx), trachea, bronchus, kidney and renal pelvis, urinary bladder, and cervix, and causes acute myeloid leukemia.
Visit smokefree.gov to learn how you can quit smoking.
Secondhand Smoke
Adults who are exposed to secondhand smoke at home or at work increase their risk of developing lung cancer by 20% to 30%. Concentrations of many cancer-causing and toxic chemicals are higher in secondhand smoke than in the smoke inhaled by smokers.
Protecting Your Skin
Skin cancer is the most common kind of cancer in the United States. Exposure to ultraviolet (UV) rays from the sun and tanning beds appears to be the most important environmental factor involved with developing skin cancer. To help prevent skin cancer while still having fun outdoors, protect yourself by seeking shade, applying sunscreen, and wearing sunprotective clothing, a hat, and sunglasses.
DETECTING MELANOMA
Melanoma is the most serious type of skin cancer. Often the first sign of melanoma is a change in the size, shape, color, or feel of a mole. Most melanomas have a black or black-blue area. Melanoma may also appear as a new mole. It may be black, abnormal, or “ugly looking.”
Thinking of “ ABCDE ” can help you remember what to watch for:
- A symmetry – the shape of one half does not match the other
- B order – the edges are ragged, blurred or irregular
- C olor – the color is uneven and may include shades of black, brown and tan
- D iameter – there is a change in size, usually an increase (larger than 6 millimeters or about 1/4 inch)
- E volving – the mole has changed (in size, color, shape; it may start to itch or bleed) over the past few weeks or months
Limiting Alcohol Intake
Drinking alcohol raises the risk of some cancers. Drinking any kind of alcohol can contribute to cancers of the mouth and throat, larynx (voice box), esophagus, colon and rectum, liver, and breast (in women). The less alcohol you drink, the lower the risk of cancer.
Studies around the world have shown that drinking alcohol regularly increases the risk of getting mouth, voice box, and throat cancers.
A large number of studies provide strong evidence that drinking alcohol is a risk factor for primary liver cancer, and more than 100 studies have found an increased risk of breast cancer with increasing alcohol intake. The link between alcohol consumption and colorectal (colon) cancer has been reported in more than 50 studies.
Keeping a Healthy Weight
Research has shown that being overweight or obese substantially raises a person’s risk of getting endometrial (uterine), breast, prostate, and colorectal cancers. Overweight is defined as a body mass index (BMI) of 25 to 29, and obesity is defined as a BMI of 30 or higher. You can learn more about eating healthy and maintaining a healthy weight in chapters 9 and 10.
Types of Cancer Treatment
Figure \(\PageIndex{3}\). Source: National Cancer Institute - https://www.cancer.gov/about-cancer/treatment/types
There are many types of cancer treatment. The types of treatment will depend on the type of cancer and how advanced it is. Some people with cancer will have only one treatment. But most people have a combination of treatments, such as surgery with chemotherapy and/or radiation therapy.
Surgery
When used to treat cancer, surgery is a procedure in which a surgeon removes cancer from your body. Learn the different ways that surgery is used against cancer and what you can expect before, during, and after surgery.
Radiation Therapy
Radiation therapy is a type of cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. Learn about the types of radiation, why side effects happen, which ones you might have, and more.
Chemotherapy
Chemotherapy is a type of cancer treatment that uses drugs to kill cancer cells. Learn how chemotherapy works against cancer, why it causes side effects, and how it is used with other cancer treatments.
Immunotherapy
Immunotherapy is a type of treatment that helps your immune system fight cancer. Get information about the types of immunotherapy and what you can expect during treatment.
Targeted Therapy
Targeted therapy is a type of cancer treatment that targets the changes in cancer cells that help them grow, divide, and spread. Learn how targeted therapy works against cancer and about common side effects that may occur.
Hormone Therapy
Hormone therapy is a treatment that slows or stops the growth of breast and prostate cancers that use hormones to grow. Learn about the types of hormone therapy and side effects that may happen.
Stem Cell Transplant
Figure \(\PageIndex{4}\). Stem Cell Transplant
Stem cell transplants are procedures that restore blood-forming stem cells in cancer patients who have had theirs destroyed by very high doses of chemotherapy or radiation therapy. Learn about the types of transplants, side effects that may occur, and how stem cell transplants are used in cancer treatment.
Precision Medicine
Precision medicine helps doctors select treatments that are most likely to help patients based on a genetic understanding of their disease. Learn about the role precision medicine plays in cancer treatment, including how genetic changes in a person's cancer are identified and used to select treatments.