12 Cancer Development

By Althea Moser

Objectives:

• Define cancer and how cancer arises
• Describe different types of cancer
• Identify cancer risks and methods for cancer prevention
• Assess personal cancer risk

What Is Cancer?

Cancer is the name given to a collection of related diseases in which 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.

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.

Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid 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 invade nearby tissues. However, some benign tumors can be quite large. When removed, they usually do not grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign tumors in the brain can be life threatening.

How Cancer Arises

Cancer is a genetic disease—that is, it 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. They can also be the result of errors that occur as cells divide or environmental exposures that cause damage to DNA, the molecules inside cells that carry genetic information and pass it on from one generation to the next. Cancer- causing environmental exposures include substances, such as the chemicals in tobacco smoke; and radiation, such as ultraviolet rays from the sun.

Each person’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur. Even within the same tumor, different cells may have different genetic changes.

In general, cancer cells have more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may be the result of the cancer, rather than its cause.

Cancer Statistics

Cancer severely impacts Americans and societies throughout the world. Cancer statistics describe what happens in large groups of people and provide a picture in time of the burden of cancer on society. Statistics indicate how many people are diagnosed with and die from cancer each year, the number of people who are currently living after a cancer diagnosis, and the average age at diagnosis. They also reveal differences among groups defined by age, sex, racial/ethnic group, geographic location, and other categories.

Although statistical trends are usually not directly applicable to individual patients, they are essential for governments, policymakers, health professionals, and researchers to understand the impact of cancer on the population and to develop strategies to address the challenges that cancer poses to society. Statistical trends are also important for measuring the success of efforts to control and manage cancer.

Statistics at a Glance: The Burden of Cancer in the United States

• In 2016, an estimated 1,685,210 new cases of cancer will be diagnosed in the United States, and 595,690 people will die from the disease.

• The most common cancers in 2016 are projected to be breast cancer, lung and bronchus cancer, prostate cancer, colon and rectum cancer, bladder cancer, melanoma of the skin, non-Hodgkin lymphoma, thyroid cancer, kidney and renal pelvis cancer, leukemia, endometrial cancer, and pancreatic cancer.

• The number of new cases of cancer (cancer incidence) is 454.8 per 100,000 men and women per year (based on 2008–2012 cases).

• The number of cancer deaths (cancer mortality) is 171.2 per 100,000 men and women per year (based on 2008–2012 deaths).

• Cancer mortality is higher among men than women (207.9 per 100,000 men and 145.4 per 100,000 women). It is highest in African American men (261.5 per 100,000) and lowest in Asian/Pacific Islander women (91.2 per 100,000) per year (based on 2008–2012 deaths).

• The number of people living beyond a cancer diagnosis reached nearly 14.5 million in 2014 and is expected to rise to almost 19 million by 2024.

• Approximately 39.6 percent of men and women will be diagnosed with cancer during their lifetimes (based on 2010-2012 data).

• In 2014, an estimated 15,780 children and adolescents, aged from 0 to 19, were diagnosed with cancer and 1,960 died of the disease.

• National expenditures for cancer care in the United States totaled nearly $125 billion in 2010 and could reach $156 billion in 2020.

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 may also be described by the type of cell that formed them, such as an epithelial cell or a squamous cell.

Some types of cancer are:

Breast Cancer

The breast is made up of glands called lobules that can make milk and thin tubes called ducts that carry the milk from the lobules to the nipple. Breast tissue also contains fat and connective tissue, lymph nodes, and blood vessels.

The most common type of breast cancer is ductal carcinoma, which begins in the cells of the ducts. Breast cancer can also begin in the cells of the lobules and in other tissues in the breast. Ductal carcinoma in situ is a condition in which abnormal cells are found in the lining of the ducts but have not spread outside the duct. Breast cancer that has spread from where it began in the ducts or lobules to surrounding tissue is called invasive breast cancer. In inflammatory breast cancer, the breast looks red and swollen and feels warm because the cancer cells block the lymph vessels in the skin.

In the United States, breast cancer is the second most common cancer in women after skin cancer. It can occur in both men and women, but it is rare in men. Each year there are about 100 times more new cases of breast cancer in women than in men.

Some screening tests for breast cancer include:

• Clinical breast exams and regular breast self-exams

Routine examinations of the breasts by health care providers or by women themselves have not been shown to reduce deaths from breast cancer. However, if a woman or her health care provider notices a lump or other unusual change in the breast, it is important for her to get it checked out.

The following link explains how to perform a Breast Self-Exam:

Breast Self-Exam (BSE): https://www.nationalbreastcancer.org/breast-self-exam

• Mammography

This screening method for breast cancer has been shown to reduce mortality from the disease among women aged from 40 to 74, especially those aged 50 or older.

• Breast MRI

This imaging test is often used for women who carry a harmful mutation in the BRCA1 gene or the BRCA2 gene; such women have a high risk of developing breast cancer, as well as increased risk for other cancers.

Cervical Cancer

The cervix is the lower, narrow end of the uterus, the organ where a fetus grows. The cervix leads from the uterus to the vagina, also known as the birth canal.

The main types of cervical cancer are squamous cell carcinoma and adenocarcinoma. Squamous cell carcinoma begins in the thin, flat cells that line the cervix. Adenocarcinoma begins in cervical cells that make mucus and other fluids.

Long-lasting infections with certain types of human papillomavirus (HPV) cause almost all cases of cervical cancer. Vaccines that protect against infection with these types of HPV can greatly reduce the risk of cervical cancer.

Screening tests:

• Pap test and human papillomavirus (HPV) testing

Having a Pap test to check for abnormal cells in the cervix, or a test to check for HPV, can find cells that may become cervical cancer. These cells can be treated before cancer forms. Testing is generally recommended to begin at age 21 and to end at age 65, as long as recent results have been normal.

Cervical cancer can usually be cured if it is found and treated in the early stages.

Colorectal Cancer

Colorectal cancer is cancer that starts in the colon or rectum. The colon and the rectum are parts of the large intestine, which is the lower part of the body’s digestive system. During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from the food and stores waste matter called stool. Stool moves from the colon into the rectum before it leaves the body.

Most colorectal cancers are adenocarcinomas, cancers that begin in cells that make and release mucus and other fluids. Colorectal cancer often begins as an abnormal colon growth called a polyp, which may form on the inner wall of the colon or rectum. Some polyps may develop into cancer over time. Finding and removing polyps can prevent colorectal cancer.

Colorectal cancer is the third most common type of cancer in men and women in the United States.

Screening tests:

• Colonoscopy, sigmoidoscopy, and high-sensitivity fecal occult blood tests (FOBTs)

Deaths from colorectal cancer have decreased with the use of colonoscopies and fecal occult blood tests, which check for blood in the stool. Colonoscopy and sigmoidoscopy also help prevent colorectal cancer because they can detect polyps that can be removed before they develop into cancer.

Expert groups generally recommend that people who are at average risk for colorectal cancer have screening beginning at age 50 through age 75.

Lung Cancer

Most lung cancer diagnoses are either non- small cell lung cancer or small cell lung cancer, depending on the way the cells look under a microscope. Non-small cell lung cancer is much more common than small cell lung cancer.

Most cases of lung cancer are caused by smoking. Lung cancer is the leading cause of death from cancer in the United States.

For most patients with lung cancer, current treatments do not cure the cancer.

Screening test:

• Low-dose helical computed tomography

This test, which is used to screen for lung cancer, has been shown to reduce lung cancer deaths among heavy smokers aged from 55 to 74.

Prostate Cancer

The prostate gland makes fluid that forms part of semen. The prostate lies just below the bladder in front of the rectum. It surrounds the urethra, the tube that carries urine and semen through the penis and out of the body.

Prostate cancer is the most common cancer in men in the United States, after skin cancer, and the second leading cause of death. Prostate cancer occurs more often in African-American men than in white men. African-American men with prostate cancer are more likely to die from the disease than white men with prostate cancer.

Almost all prostate cancers are adenocarcinomas, cancers that begin in cells that make and release mucus and other fluids. Prostate cancer often has no early symptoms. Advanced prostate cancer can cause men to urinate more often or have a weaker flow of urine, but these symptoms can also be caused by benign prostate conditions.

Prostate cancer usually grows very slowly. Most men with prostate cancer are older than 65 years and do not die from the disease. Finding and treating prostate cancer before symptoms occur may not improve a patient’s health or help him live longer. Men are advised to consult their doctor about their risk of prostate cancer and whether they need screening tests.

Screening test:

• PSA test

This blood test, which is often done along with a digital rectal exam, is able to detect prostate cancer at an early stage. However, expert groups no longer recommend routine PSA testing for most men because studies have shown that it has little or no effect on prostate cancer deaths and leads to over-diagnosis and over-treatment.

Skin Cancer

Skin cancer is the most common type of cancer. It usually forms in skin that has been exposed to sunlight but can occur anywhere on the body.

Skin consists of several layers. Skin cancer begins in the epidermis, or outer layer, which is made up of squamous cells, basal cells, and melanocytes.

There are several different types of skin cancer. Squamous cell and basal cell skin cancers are sometimes called nonmelanoma skin cancers.

Nonmelanoma skin cancer usually responds to treatment and rarely spreads to other parts of the body.

Melanoma is more aggressive than most other types of skin cancer. Unless melanoma is diagnosed early, it is likely to invade nearby tissues and spread to other parts of the body. The number of cases of melanoma increases each year. Only 2 percent of all skin cancers are melanoma, but it causes the most deaths from skin cancer.

Screening test:

• Skin exams

Doctors often recommend that people who are at risk for skin cancer examine their skin regularly or have a health care provider do so. Such exams have not been shown to decrease the risk of dying from skin cancer, and they may lead to over-treatment. However, people should be aware of changes in their skin, such as a new mole or a change to an existing mole, and report these to their doctor promptly.

Testicular Cancer

The testicles are two glands inside the scrotum, a sac of loose skin below the penis. The testicles make sperm and the hormone testosterone.

Testicular cancer is the most common cancer in men aged from 15 to 34 years. The two main types of testicular tumors are seminoma and nonseminoma.

Nonseminomas tend to grow and spread more quickly than seminomas.

The most common sign of testicular cancer is a lump or swelling in the testicle. Most testicular cancers can be cured, even if they are diagnosed at an advanced stage.

Treatment for testicular cancer can cause infertility by decreasing the amount of sperm made by the body. Men who want to have children may want to use sperm banking to store sperm before they begin treatment.

Screening test:

• There is no standard or routine screening test for testicular cancer. Most often, testicular cancer is first found by men themselves, either by chance or during self-exam. Sometimes the cancer is found by a doctor during a routine physical exam.

The following video explains how to perform a testicular self-exam:

Testicular Self-Exam

Leukemia

Leukemia is cancer of the blood cells. Most blood cells form in the bone marrow. In leukemia, immature blood cells become cancer. These cells do not work the way they should and crowd out the healthy blood cells in the bone marrow.

Different types of leukemia depend on the type of blood cell that becomes cancer. For example, lymphoblastic leukemia is a cancer of the lymphoblasts, white blood cells that fight infection. White blood cells are the most common type of blood cell to become cancer. But red blood cells, cells that carry oxygen from the lungs to the rest of the body, and platelets, cells that clot the blood, may also become cancerous.

Leukemia occurs most often in adults older than 55 years, but it is also the most common cancer in children younger than 15 years.

Leukemia can be either acute or chronic. Acute leukemia is a fast-growing cancer that usually gets worse quickly. Chronic leukemia is a slower-growing cancer that gets worse slowly over time. The treatment and prognosis for leukemia depend on the type of blood cell affected and whether the leukemia is acute or chronic.

Lymphoma

Lymphoma is cancer that begins in cells of the lymph system. The lymph system is part of the immune system, which helps the body fight infection and disease. Because lymph tissue is found all through the body, lymphoma can begin almost anywhere.

The two main types of lymphoma are Hodgkin lymphoma and non-Hodgkin lymphoma (NHL). These can occur in both children and adults. The treatment and probability of a cure depend on the stage and the type of lymphoma.

Risk Factors for Cancer

It is usually impossible to know why one person develops cancer and another does not. But research has shown that certain risk factors may increase a person’s chances of developing cancer. There are also factors—called protective risk factors, or just protective factors—that are linked to a lower risk of cancer.

Cancer risk factors include exposure to chemicals or other substances, as well as certain behaviors. They also include circumstances that 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 risks, as well as 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 do not. These studies may show that those 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.

On their own, such studies 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 false beliefs 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.

Although some risk factors can be avoided, others—such as growing older—cannot.

Limiting exposure to avoidable risk factors may lower a person’s risk of developing certain cancers.

Some of the most studied risk factors for cancer are listed below.

Age

Advancing age is the most important risk factor for cancer overall, and for many specific types of cancer. According to the most recent statistical data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results program, the median age of a cancer diagnosis is 66 years. This means that half of cancer cases occur in people below this age and half in people above this age. One-quarter of new cancer cases are diagnosed in people aged from 65 to 74.

But the disease can occur at any age. For example, bone cancer is most frequently diagnosed among people under age 20, with more than one-fourth of cases occurring in this age group. And 10 percent of leukemias are diagnosed in children and adolescents under 20 years of age, whereas only 1 percent of cancer overall is diagnosed in that age group.

Alcohol

Drinking alcohol can increase a person’s risk of cancer of the mouth, throat, esophagus, larynx (voice box), liver, and breast. The more a person consumes alcohol, the higher his or her risk. The risk of cancer is much higher for those who drink alcohol and also use tobacco.

Doctors advise people who drink to do so in moderate amounts. The federal government’s Dietary Guidelines for Americans defines moderate alcohol drinking as up to one drink per day for women and up to two drinks per day for men.

It has been suggested that certain substances in red wine, such as resveratrol, have anticancer properties. However, no evidence exists that drinking red wine reduces the risk of cancer.

Cancer-Causing Substances in the Environment

Cancer is caused by changes to certain genes that alter the way our cells function. Some of these genetic changes occur naturally when DNA is replicated during the process of cell division. But others are the result of environmental exposures that damage DNA. These exposures may include substances known as carcinogens, any substance that causes cancer, such as the chemicals in tobacco smoke; and radiation, such as ultraviolet rays from the sun.

People can avoid some cancer-causing exposures, such as tobacco smoke and the sun’s rays. But others are harder to avoid, especially if they are found in the air, water, and food, or the materials people use to do their jobs. Scientists are studying which exposures may cause or contribute to the development of cancer. Understanding which exposures are harmful, and where they are found, may help people avoid them.

Simply because a substance has been designated as a carcinogen, however, that does not mean that the substance will necessarily cause cancer. Many factors influence whether a person exposed to a carcinogen will develop cancer, including the amount and duration of the exposure and the individual’s genetic background.

Diet

Many studies have looked at the possibility that specific dietary components or nutrients are associated with increases or decreases in cancer risk. Studies of cancer cells in the laboratory and of animal models have sometimes provided evidence that isolated compounds may be carcinogenic, or have anticancer activity.

But with few exceptions, studies of human populations have not yet shown definitively that any dietary component causes or protects against cancer. Sometimes the results of epidemiologic studies, which compare the diets of people with and without cancer have indicated that people with and without cancer differ in their intake of a particular dietary component.

However, these results show only that the dietary component is associated with a change in cancer risk, not that the dietary component is responsible for, or causes, the change in risk. For example, participants with and without cancer could differ in other ways besides their diet, and it is possible that some other difference accounts for the variance in cancer risk.

Hormones

Estrogens, a group of female sex hormones, are known human carcinogens. Although these hormones have essential physiological roles in both females and males, they have also been associated with an increased risk of certain cancers. For instance, taking combined menopausal hormone therapy (estrogen plus progestin, which is a synthetic version of the female hormone progesterone) can increase a woman’s risk of breast cancer. Menopausal hormone therapy with estrogen alone increases the risk of endometrial cancer and is used only in women who have had a hysterectomy.

A woman who is considering menopausal hormone therapy should discuss the possible risks and benefits with her doctor.

Studies have also shown that a woman’s risk of breast cancer is related to the estrogen and progesterone made by her ovaries, known as endogenous estrogen and progesterone. Being exposed for a long time and/or to high levels of these hormones has been linked to an increased risk of breast cancer. Increases in exposure can be caused by starting menstruation early, going through menopause late, being older at first pregnancy, and never having given birth. Conversely, having given birth is a protective factor for breast cancer.

Obesity

People who are obese may have an increased risk of several types of cancer, including cancers of the breast (in women who have been through menopause), colon, rectum, esophagus, kidney, pancreas, gallbladder, and the lining of the uterus, called the endometrium.

Conversely, eating a healthy diet, being physically active, and maintaining a healthy weight may reduce the risk of some cancers. These healthy behaviors also lessen the risk of other illnesses, such as heart disease, type II diabetes, and high blood pressure.

Sunlight

The sun, sunlamps, and tanning booths all give off ultraviolet (UV) radiation. Exposure to UV radiation causes early aging of the skin and skin damage that can lead to skin cancer.

People of all ages should limit the amount of time they spend in the sun, especially between mid-morning and late afternoon, and avoid other sources of UV radiation, such as tanning beds. It is important to keep in mind that UV radiation is reflected by sand, water, snow, and ice and can go through windshields and windows.

The best way to lessen UV damage when spending time in the sun is to wear long sleeves, long pants, a hat with a wide brim, and sunglasses with lenses that absorb UV radiation. Sunscreen with a sun protection factor (SPF) of at least 15 may help prevent skin cancer but does not work as well as staying out of the sun and wearing protective clothing.

Tobacco

Tobacco use is a leading cause of cancer and of death from cancer. People who use tobacco products, or are regularly exposed to environmental tobacco smoke (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, mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon and rectum, and cervix, as well as acute myeloid leukemia. People who use smokeless tobacco, such as snuff or chewing tobacco, have increased risks of cancers of the mouth, esophagus, and pancreas.

No level of tobacco use is safe. 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.

Cancer Prevention Overview

Cancer prevention is action taken to lower the chance of getting cancer. In addition to the physical problems and emotional distress caused by cancer, the high costs of care are also a burden to patients, their families, and to the public. Preventative measures can lower the number of new cases and cancer deaths, and reduce the burden of cancer on society.

Scientists are studying ways to prevent cancer, including the following:

• avoiding or controlling factors known to cause cancer
• improving diet and adopting a healthier lifestyle
• finding precancerous conditions early
• incorporating chemo prevention: the use of medicines that treat precancerous conditions or prevent cancer from starting

Cancer Treatment

Patients and their doctors must choose from a plethora of cancer treatments. The types of treatment a patient receives depend on the type of cancer a person has 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.

They may also undergo immunotherapy, targeted therapy, or hormone therapy.

Clinical trials are also an option for some patients. Clinical trials are research studies that involve people. Understanding what they are and how they work can help patients decide if taking part in a trial is a good option.

When seeking treatment for cancer, patients have a lot to learn and consider. It is normal for them to feel overwhelmed and confused. Talking with their doctor and learning all they can about their treatment options, including clinical trials, can help them make a decision they feel good about.

Assessing Your Personal Risk of Cancer

Complete the following Lab to assess your personal risk of cancer, and submit it per your instructor’s directions:

Assess Your Risk of Cancer

Source:

The website of the National Cancer Institute (https://www.cancer.gov) Copyright Disclaimer:

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