cancer

Cancer : Overview / Facts / Causes / Treatment / Research

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.

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 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.

Differences between Cancer Cells and Normal Cells

Image result for cancer cell vs normal cell

Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive. One important difference is that cancer cells are less specialized than normal cells. That is, whereas normal cells mature into very distinct cell types with specific functions, cancer cells do not. This is one reason that, unlike normal cells, cancer cells continue to divide without stopping.

In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded cells.

Cancer cells may be able to influence the normal cells, molecules, and blood vessels that surround and feed a tumor—an area known as the microenvironment. For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors.

Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions. Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to “hide” from the immune system.

Tumors can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.

Cancer facts
  • Cancer is the uncontrolled growth of abnormal cells anywhere in a body.
  • There are over 200 types of cancer.
  • Anything that may cause a normal body cell to develop abnormally potentially can cause cancer; general categories of cancer-related or causative agents are as follows: chemical or toxic compound exposures, ionizing radiation, some pathogens, and human genetics.
  • Cancer symptoms and signs depend on the specific type and grade of cancer; although general signs and symptoms are not very specific the following can be found in patients with different cancers: fatigue, weight loss, pain, skin changes, change in bowel or bladder function, unusual bleeding, persistent cough or voice change, fever, lumps, or tissue masses.
  • Although there are many tests to screen and presumptively diagnose cancer, the definite diagnosis is made by examination of a biopsy sample of suspected cancer tissue.
  • Cancer staging is often determined by biopsy results and helps determine the cancer type and the extent of cancer spread; staging also helps caregivers determine treatment protocols. In general, in most staging methods, the higher the number assigned (usually between 0 to 4), the more aggressive the cancer type or more widespread is the cancer in the body. Staging methods differ from cancer to cancer and need to be individually discussed with your health care provider.
  • Treatment protocols vary according to the type and stage of the cancer. Most treatment protocols are designed to fit the individual patient’s disease. However, most treatments include at least one of the following and may include all: surgery, chemotherapy, and radiation therapy.
  • There are many listed home remedies and alternative treatments for cancers but patients are strongly recommended to discuss these before use with their cancer doctors.
  • The prognosis of cancer can range from excellent to poor. The prognosis depends on the cancer type and its staging with those cancers known to be aggressive and those staged with higher numbers (3 to 4) often have a prognosis that ranges more toward poor.
When Cancer Spreads ?

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.

Treatment may help prolong the lives of some people with metastatic cancer. In general, though, the primary goal of treatments for metastatic cancer is to control the growth of the cancer or to relieve symptoms caused by it. Metastatic tumors can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease.

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.

An even more serious condition is carcinoma in situ. Although it is sometimes called cancer, carcinoma in situ is not cancer because the abnormal cells do not spread beyond the original tissue. That is, they do not invade nearby tissue the way that cancer cells do. But, because some carcinomas in situ may become cancer, they are usually treated.

Drawing of four panels showing how normal cells may become cancer cells. The first panel shows normal cells. The second and third panels show abnormal cell changes called hyperplasia and dysplasia. The fourth panel shows cancer cells.

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.

Credit: Terese Winslow
Symptoms of Cancer
Some of the symptoms that cancer may cause include:

Breast changes

  • Lump or firm feeling in your breast or under your arm
  • Nipple changes or discharge
  • Skin that is itchy, red, scaly, dimpled, or puckered

Bladder changes

  • Trouble urinating
  • Pain when urinating
  • Blood in the urine

Bleeding or bruising, for no known reason

Bowel changes 

  • Blood in the stools
  • Changes in bowel habits

Cough or hoarseness that does not go away

Eating problems

  • Pain after eating (heartburn or indigestion that doesn’t go away)
  • Trouble swallowing
  • Belly pain
  • Nausea and vomiting
  • Appetite changes

Fatigue that is severe and lasts

Fever or night sweats for no known reason

Mouth changes

  • A white or red patch on the tongue or in your mouth
  • Bleeding, pain, or numbness in the lip or mouth

Neurological problems

  • Headaches
  • Seizures
  • Vision changes
  • Hearing changes
  • Drooping of the face

Skin changes

  • A flesh-colored lump that bleeds or turns scaly
  • A new mole or a change in an existing mole
  • A sore that does not heal
  • Jaundice (yellowing of the skin and whites of the eyes)

Swelling or lumps anywhere such as in the neck, underarm, stomach, and groin

Weight gain or weight loss for no known reason

Factors That are Known to Increase the Risk of Cancer
Cigarette Smoking and Tobacco Use

Tobacco use is strongly linked to an increased risk for many kinds of cancer. Smoking cigarettes is the leading cause of the following types of cancer:

  • Acute myelogenous leukemia (AML).
  • Bladder cancer.
  • Cervical cancer.
  • Esophageal cancer.
  • Kidney cancer.
  • Lung cancer.
  • Oral cavity cancer.
  • Pancreatic cancer.
  • Stomach cancer.

Not smoking or quitting smoking lowers the risk of getting cancer and dying from cancer. Scientists believe that cigarette smoking causes about 30% of all cancer deaths in the United States.

Infections

Certain viruses and bacteria are able to cause cancer. Viruses and other infection -causing agents cause more cases of cancer in the developing world (about 1 in 4 cases of cancer) than in developed nations (less than 1 in 10 cases of cancer). Examples of cancer-causing viruses and bacteria include:

  • Human papillomavirus (HPV) increases the risk for cancers of the cervix, penis, vagina, anus, and oropharynx.
  • Hepatitis B and hepatitis C viruses increase the risk for liver cancer.
  • Epstein-Barr virus increases the risk for Burkitt lymphoma.
  • Helicobacter pylori increases the risk for gastric cancer.

Two vaccines to prevent infection by cancer-causing agents have already been developed and approved by the U.S. Food and Drug Administration (FDA). One is a vaccine to prevent infection with hepatitis B virus. The other protects against infection with strains of human papillomavirus (HPV) that cause cervical cancer. Scientists continue to work on vaccines against infections that cause cancer.

Radiation

Being exposed to radiation is a known cause of cancer. There are two main types of radiation linked with an increased risk for cancer:

  • Ultraviolet radiation from sunlight: This is the main cause of nonmelanoma skin cancers.
  • Ionizing radiation including:
    • Medical radiation from tests to diagnose cancer such as x-rays, CT scans, fluoroscopy, and nuclear medicine scans.
    • Radon gas in our homes.

Scientists believe that ionizing radiation causes leukemia, thyroid cancer, and breast cancerin women. Ionizing radiation may also be linked to myeloma and cancers of the lung, stomach, colon, esophagus, bladder, and ovary. Being exposed to radiation from diagnostic x-rays increases the risk of cancer in patients and x-ray technicians.

The growing use of CT scans over the last 20 years has increased exposure to ionizing radiation. The risk of cancer also increases with the number of CT scans a patient has and the radiation dose used each time.

Immunosuppressive Medicines After Organ Transplant

Immunosuppressive medicines are used after an organ has been transplanted from one person to another. These medicines stop an organ that has been transplanted from being rejected. These medicines decrease the body’s immune response to help keep the organ from being rejected. Immunosuppressive medicines are linked to an increased risk of cancer because they lower the body’s ability to keep cancer from forming. The risk of cancer, especially cancer caused by a virus, is higher in the first 6 months after organ transplant, but the risk lasts for many years.

Environmental Risk Factors

Being exposed to chemicals and other substances in the environment has been linked to some cancers:

  • Links between air pollution and cancer risk have been found. These include links between lung cancer and secondhand tobacco smoke, outdoor air pollution, and asbestos.
  • Drinking water that contains a large amount of arsenic has been linked to skin, bladder, and lung cancers.

Studies have been done to see if pesticides and other pollutants increase the risk of cancer. The results of those studies have been unclear because other factors can change the results of the studies.

How is Cancer Risk Measured?

Cancer risk is measured in different ways. The findings from surveys and studies about cancer risk are studied and the results are explained in different ways. Some of the ways risk is explained include absolute risk relative risk , and odds ratios .

  • Absolute risk

    This is the risk a person has of developing a disease, in a given population (for example, the entire U.S. population) over a certain period of time. Researchers estimate the absolute risk by studying a large number of people that are part of a certain population (for example, women in a given age group). Researchers count the number of people in the group who get a certain disease over a certain period of time. For example, a group of 100,000 women between the ages of 20 and 29 are observed for one year, and 4 of them get breast cancer during that time. This means that the one-year absolute risk of breast cancer for a woman in this age group is 4 in 100,000, or 4 chances in 100,000.

  • Relative risk

    This is often used in research studies to find out whether a trait or a factor can be linked to the risk of a disease. Researchers compare two groups of people who are a lot alike. However, the people in one of the groups must have the trait or factor being studied (they have been “exposed”). The people in the other group do not have it (they have not been exposed). To figure out relative risk, the percentage of people in the exposed group who have the disease is divided by the percentage of people in the unexposed group who have the disease.

    Relative risks can be:

    • Larger than 1: The trait or factor is linked to an increase in risk.
    • Equal to 1: The trait or factor is not linked to risk.
    • Less than 1: The trait or factor is linked to a decrease in risk.

    Relative risks are also called risk ratios.

  • Odds ratio

    In some types of studies, researchers don’t have enough information to figure out relative risks. They use something called an odds ratio instead. An odds ratio can be an estimate of relative risk.

    One type of study that uses an odds ratio instead of relative risk is called a case-control study. In a case-control study, two groups of people are compared. However, the individuals in each group are chosen based on whether or not they have a certain disease. Researchers look at the odds that the people in each group were exposed to something (a trait or factor) that might have caused the disease. Odds describes the number of times the trait or factor was present or happened, divided by the number of times it wasn’t present or didn’t happen. To get an odds ratio, the odds for one group are divided by the odds for the other group.

    Odds ratios can be:

    • Larger than 1: The trait or factor is linked to an increase in risk.
    • Equal to 1: The trait or factor is not linked to risk.
    • Less than 1: The trait or factor is linked to a decrease in risk.

Looking at traits and exposures in people with and without cancer can help find possible risk factors. Knowing who is at an increased risk for certain types of cancer can help doctors decide when and how often they should be screened.

Types of Cancer Treatment

There are many types of cancer treatment. The types of treatment that you receive will depend on the type of cancer you have and how advanced it is.

Group of surgeons in caps and masks

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.

Nurse preparing a patient for radiation therapy

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.

Doctor administering chemotherapy

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.

Researcher looking at a computer screen

Immunotherapy to Treat Cancer

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.

silhouettes of people, a DNA strand, and a bottle of medication

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.

Woman leaning her head against a man's chest

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.

patient receiving stem cell transplant

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.

Challenges in Cancer Treatment Research

Although many advances in cancer treatment have been made in recent decades, numerous challenges remain before the goal of providing the best possible outcome for all patients diagnosed with cancer can be achieved.

For example, developing targeted therapies requires the identification of good molecular targets—that is, targets that play a key role in cancer cell growth and survival—and the design and development of drugs that effectively “hit”, or bind to, those targets. However, some potential targets that have been identified appear to lack places to which an anticancer drug can bind and, therefore, have been called “undruggable.” Finding ways to design drugs that effectively hit these targets is a major challenge.

Drug resistance—either to traditional chemotherapy drugs or to newer targeted therapies—is another challenge in cancer treatment. More research is needed to uncover the mechanisms of drug resistance and identify ways to overcome it.

The genomic characterization of tumors has provided both new opportunities for cancer treatment and new challenges. The discovery that each individual’s cancer has a unique constellation of gene mutations and other alterations increases the complexity of identifying treatments that are likely to work best for a given person’s cancer. However, even within a single patient, different parts of a single tumor, or different metastatic tumor nodules in the same patient, may not be identical in terms of the molecular changes that are present. This raises the possibility that a drug might be effective in one part of a person’s tumor but not in another.

Moreover, although recent advances in immunotherapy have been dramatic, this approach to treating cancer is still in its infancy. Many challenges remain, including how to optimize the immune response to eradicate cancer while avoiding runaway responses that cause autoimmune damage to normal tissues. An additional challenge is determining why current immunotherapies work in some patients but not in others.

Many challenges also remain in optimizing cancer treatment with conventional chemotherapy drugs, radiation therapy, and surgery. Research on the identification and development of additional chemotherapeutic agents is needed, as is research to refine the delivery of lethal doses of radiation therapy to tumors while sparing the surrounding normal tissues from harm. Another challenge is the development of ever more effective treatments to alleviate the side effects of all forms of cancer therapy.

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