Cancer

Cancer

Cancer is a class of diseases characterized by out-of-control cell growth. There are over 100 different types of cancer, and each is classified by the type of cell that is initially affected. Cancer harms the body when damaged cells divide uncontrollably to form lumps or masses of tissue called tumors (except in the case of leukemia where cancer prohibits normal blood function by abnormal cell division in the blood stream). Tumors can grow and interfere with the digestive, nervous, and circulatory systems, and they can release hormones that alter body function. Tumors that stay in one spot and demonstrate limited growth are generally considered to be benign.

More dangerous, or malignant, tumors form when two things occur:

• a cancerous cell manages to move throughout the body using the blood or lymph systems, destroying healthy tissue in a process called invasion
• that cell manages to divide and grow, making new blood vessels to feed itself in a process called angiogenesis.

When a tumor successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a serious condition that is very difficult to treat. 

In 2007, cancer claimed the lives of about 7.6 million people in the world. Physicians and researchers who specialize in the study, diagnosis, treatment, and prevention of cancer are called oncologists.

What causes cancer?

 Cancer is ultimately the result of cells that uncontrollably grow and do not die. Normal cells in the body follow an orderly path of growth, division, and death. Programmed cell death is called apoptosis, and when this process breaks down, cancer begins to form. Unlike regular cells, cancer cells do not experience programmatic death and instead continue to grow and divide. This leads to a mass of abnormal cells that grows out of control.

Genes - the DNA type

Cells can experience uncontrolled growth if there are damages or mutations to DNA, and therefore, damage to the genes involved in cell division. Four key types of gene are responsible for the cell division process: oncogenes tell cells when to divide, tumor suppressor genes tell cells when not to divide, suicide genes control apoptosis and tell the cell to kill itself if something goes wrong, and DNA-repair genes instruct a cell to repair damaged DNA.

Cancer occurs when a cell's gene mutations make the cell unable to correct DNA damage and unable to commit suicide. Similarly, cancer is a result of mutations that inhibit oncogene and tumor suppressor gene function, leading to uncontrollable cell growth. 

Carcinogens

Carcinogens are a class of substances that are directly responsible for damaging DNA, promoting or aiding cancer. Tobacco, asbestos, arsenic, radiation such as gamma and x-rays, the sun, and compounds in car exhaust fumes are all examples of carcinogens. When our bodies are exposed to carcinogens, free radicals are formed that try to steal electrons from other molecules in the body. Theses free radicals damage cells and affect their ability to function normally.

Genes - the family type

Cancer can be the result of a genetic predisposition that is inherited from family members. It is possible to be born with certain genetic mutations or a fault in a gene that makes one statistically more likely to develop cancer later in life.

What are the symptoms of cancer?

Cancer symptoms are quite varied and depend on where the cancer is located, where it has spread, and how big the tumor is. Some cancers can be felt or seen through the skin - a lump on the breast or testicle can be an indicator of cancer in those locations. Skin cancer (melanoma) is often noted by a change in a wart or mole on the skin. Some oral cancers present white patches inside the mouth or white spots on the tongue.

Other cancers have symptoms that are less physically apparent. Some brain tumors tend to present symptoms early in the disease as they affect important cognitive functions. Pancreas cancers are usually too small to cause symptoms until they cause pain by pushing against nearby nerves or interfere with liver function to cause a yellowing of the skin and eyes called jaundice. Symptoms also can be created as a tumor grows and pushes against organs and blood vessels. For example, colon cancers lead to symptoms such as constipation, diarrhea, and changes in stool size. Bladder or prostate cancers cause changes in bladder function such as more frequent or infrequent urination.

As cancer cells use the body's energy and interfere with normal hormone function, it is possible to present symptoms such as fever, fatigue, excessive sweating, anemia, and unexplained weight loss. However, these symptoms are common in several other maladies as well. For example, coughing and hoarseness can point to lung or throat cancer as well as several other conditions.

When cancer spreads, or metastasizes, additional symptoms can present themselves in the newly affected area. Swollen or enlarged lymph nodes are common and likely to be present early. If cancer spreads to the brain, patients may experience vertigo, headaches, or seizures. Spreading to the lungs may cause coughing and shortness of breath. In addition, the liver may become enlarged and cause jaundice and bones can become painful, brittle, and break easily. Symptoms of metastasis ultimately depend on the location to which the cancer has spread.

How is cancer classified?

There are five broad groups that are used to classify cancer.

Carcinomas are characterized by cells that cover internal and external parts of the body such as lung, breast, and colon cancer.

Sarcomas are characterized by cells that are located in bone, cartilage, fat, connective tissue, muscle, and other supportive tissues.

Lymphomas are cancers that begin in the lymph nodes and immune system tissues.

Leukemias are cancers that begin in the bone marrow and often accumulate in the bloodstream.

Adenomas are cancers that arise in the thyroid, the pituitary gland, the adrenal gland, and other glandular tissues.

How can cancer be prevented?

Cancers that are closely linked to certain behaviors are the easiest to prevent. For example, choosing not to smoke tobacco or drink alcohol significantly lower the risk of several types of cancer - most notably lung, throat, mouth, and liver cancer. Even if you are a current tobacco user, quitting can still greatly reduce your chances of getting cancer.

Skin cancer can be prevented by staying in the shade, protecting yourself with a hat and shirt when in the sun, and using sunscreen. Diet is also an important part of cancer prevention since what we eat has been linked to the disease. Physicians recommend diets that are low in fat and rich in fresh fruits and vegetables and whole grains.

Certain vaccinations have been associated with the prevention of some cancers. For example, many women receive a vaccination for the human papillomavirus because of the virus's relationship with cervical cancer. Hepatitis B vaccines prevent the hepatitis B virus, which can cause liver cancer.

Some cancer prevention is based on systematic screening in order to detect small irregularities or tumors as early as possible even if there are no clear symptoms present. Breast self-examination, mammograms, testicular self-examination, and Pap smears are common screening methods for various cancers.

Cancer Staging

1.       What is staging?

Staging describes the severity of a person’s cancer based on the extent of the original (primary) tumor and whether or not cancer has spread in the body. Staging is important for several reasons:

• Staging helps the doctor plan the appropriate treatment.
• The stage can be used to estimate the person’s prognosis.
• Knowing the stage is important in identifying clinical trials that may be suitable for a particular patient.
• Staging helps health care providers and researchers exchange information about patients; it also gives them a common terminology for evaluating the results of clinical trials and comparing the results of different trials.

Staging is based on knowledge of the way cancer progresses. Cancer cells grow and divide without control or order, and they do not die when they should. As a result, they often form a mass of tissue called a tumor. As the tumor grows, it can invade nearby tissues and organs. Cancer cells can also break away from the tumor and enter the bloodstream or the lymphatic system. By moving through the bloodstream or lymphatic system, cancer cells can spread from the primary site to lymph nodes or to other organs, where they may form new tumors. The spread of cancer is called metastasis.

2.      What are the common elements of staging systems?

Staging systems for cancer have evolved over time. They continue to change as scientists learn more about cancer. Some staging systems cover many types of cancer; others focus on a particular type. The common elements considered in most staging systems are as follows:

·         Site of the primary tumor.

·         Tumor size and number of tumors.

·         Lymph node involvement (spread of cancer into lymph nodes).

·         Cell type and tumor grade* (how closely the cancer cells resemble normal tissue cells).

·         The presence or absence of metastasis.

3.      What is the TNM system?

The TNM system is one of the most widely used staging systems. This system has been accepted by the International Union Against Cancer (UICC) and the American Joint Committee on Cancer (AJCC). Most medical facilities use the TNM system as their main method for cancer reporting. PDQ®, NCI’s comprehensive cancer information database, also uses the TNM system.

The TNM system is based on the extent of the tumor (T), the extent of spread to the lymph nodes (N), and the presence of distant metastasis (M). A number is added to each letter to indicate the size or extent of the primary tumor and the extent of cancer spread.Primary Tumor (T)

TX       Primary tumor cannot be evaluated

T0        No evidence of primary tumor

Tis       Carcinoma in situ (CIS; abnormal cells are present but have not spread to neighboring tissue; although not cancer, CIS may become cancer and is sometimes called preinvasive cancer)

T1, T2, T3, T4 Size and/or extent of the primary tumor

Regional Lymph Nodes (N)

NX      Regional lymph nodes cannot be evaluated

N0       No regional lymph node involvement

N1, N2, N3     Involvement of regional lymph nodes (number of lymph nodes and/or extent of spread)

Distant Metastasis (M)

MX      Distant metastasis cannot be evaluated

M0      No distant metastasis

M1       Distant metastasis is present

For example, breast cancer classified as T3 N2 M0 refers to a large tumor that has spread outside the breast to nearby lymph nodes but not to other parts of the body. Prostate cancer T2 N0 M0 means that the tumor is located only in the prostate and has not spread to the lymph nodes or any other part of the body.

For many cancers, TNM combinations correspond to one of five stages. Criteria for stages differ for different types of cancer. For example, bladder cancer T3 N0 M0 is stage III, whereas colon cancer T3 N0 M0 is stage II.

Stage	Definition
Stage 0	Carcinoma in situ.
Stage I, Stage II, and Stage III	Higher numbers indicate more extensive disease: Larger tumor size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or organs adjacent to the location of the primary tumor.
Stage IV	The cancer has spread to another organ(s).

4.   Are all cancers staged with TNM classifications?

Most types of cancer have TNM designations, but some do not. For example, cancers of the brain and spinal cord are staged according to their cell type and grade. Different staging systems are also used for many cancers of the blood or bone marrow, such as lymphomas. The Ann Arbor staging classification is commonly used to stage lymphomas and has been adopted by both the AJCC and the UICC. However, other cancers of the blood or bone marrow, including most types of leukemia, do not have a clear-cut staging system. Another staging system, developed by the International Federation of Gynecology and Obstetrics, is used to stage cancers of the cervix, uterus, ovary, vagina, and vulva. This system uses the TNM format. Additionally, childhood cancers are staged using either the TNM system or the staging criteria of the Children’s Oncology Group, which conducts pediatric clinical trials.

Many cancer registries, such as NCI’s Surveillance, Epidemiology, and End Results Program (SEER), use summary staging. This system is used for all types of cancer. It groups cancer cases into five main categories:

• In situ: Abnormal cells are present only in the layer of cells in which they developed.
• Localized: Cancer is limited to the organ in which it began, without evidence of spread.
• Regional: Cancer has spread beyond the primary site to nearby lymph nodes or organs and tissues.
• Distant: Cancer has spread from the primary site to distant organs or distant lymph nodes.
• Unknown: There is not enough information to determine the stage.

5.   What types of tests are used to determine stage?

The types of tests used for staging depend on the type of cancer. Tests include the following:

• Physical exams are used to gather information about the cancer. The doctor examines the body by looking, feeling, and listening for anything unusual. The physical exam may show the location and size of the tumor(s) and the spread of the cancer to the lymph nodes and/or to other organs.

• Imaging studies produce pictures of areas inside the body. These studies are important tools in determining stage. Procedures such as x-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, and positron emission tomography (PET) scans can show the location of the cancer, the size of the tumor, and whether the cancer has spread.

• Laboratory tests are studies of blood, urine, other fluids, and tissues taken from the body. For example, tests for liver function and tumor markers (substances sometimes found in increased amounts if cancer is present) can provide information about the cancer.

• Pathology reports may include information about the size of the tumor, the growth of the tumor into other tissues and organs, the type of cancer cells, and the grade of the tumor. A biopsy may be performed to provide information for the pathology report. Cytology reports also describe findings from the examination of cells in body fluids.

• Surgical reports tell what is found during surgery. These reports describe the size and appearance of the tumor and often include observations about lymph nodes and nearby organs.