Cancer: Causes, Risk factor, Symptoms, Types and Staging

The uncontrolled growth of abnormal cells anywhere in a body is known as cancer.

Updated: June 16, 2022

The uncontrolled growth of abnormal cells anywhere in a body is known as cancer. Cancer related or causative agents could be chemical or toxic compound exposures, ionizing radiation, some pathogens, and human genetics that may cause a normal body cell to develop abnormally can cause cancer. Fatigue, weight loss, pain, skin changes, change in bowel or bladder function, unusual bleeding, persistent cough or voice change, fever, lumps, or tissue masses are most common symptoms in any type of cancer. However, signs and symptoms depend on the specific type and grade of cancer.
Although there are many blood tests and screening test for diagnosis of cancer, the definite diagnosis is made by examination of a biopsy sample of suspected cancer tissue. Biopsy results can determine the stage of a cancer and can helps determine the cancer type and the extent of cancer spread. Staging also helps the health care provider determine the suitable treatment option.
Generally in most staging methods, the higher the number of stage, 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 overall health condition of an individual patient. However, most treatments include at least one of the method as surgery, chemotherapy, and radiation therapy. Many a times all the methods may be included.
Many natural and alternative treatments are also available for cancer treatment. But, patients are strongly recommended to discuss these with their cancer doctors before using it. The prognosis depends on the cancer type and its staging which range from excellent to poor. Patient whose cancers are known to be aggressive and those staged with higher numbers that is 3 to 4, often have a prognosis that ranges more toward poor.

Causes of Cancer:

Cancer refers to cells that grow out of control and invade other tissues. Cells become cancerous due to the accumulation of defects, or mutations, in their DNA. This can be due to:

  • inherited genetic defects, such as BRCA1 and BRCA2 mutations
  • infections
  • environmental factors ,such as air pollution
  • poor lifestyle choices, such as smoking and heavy alcohol use can also damage DNA and lead to cancer.

Cells are able to detect and repair DNA damage in a healthy person. If a cell is severely damaged and cannot repair itself it undergoes death or apoptosis. when damaged cells grow, divide, and spread abnormally instead of dying as they should, then cancer occurs.
Many cancers and the abnormal cells that compose the cancer tissue are identified by the name of the tissue that the abnormal cells originated from. For example, breast cancer, lung cancer, colon cancer. When cancer cells break away from this original mass of cells, they can travel through the blood and lymph systems, and invade to other organs where they can again repeat the uncontrolled growth cycle. This process of cancer cells leaving an area and growing in another body area is termed metastatic spread or metastasis. For example, if breast cancer cells spread to a bone, it means that the individual has metastatic breast cancer to bone. This is not the same as bone cancer, which would mean the cancer had started in the bone.
The incidence of cancer and cancer types vary depending on many factors such as age, gender, race, local environmental factors, diet, and genetics. The three most common cancers in men, women, and children are as follows:

  • Men: Prostate, lung, and colorectal
  • Women: Breast, lung, and colorectal
  • Children: Leukemia, brain tumors, and lymphoma

Following is a listing of major causes of cancers.

  • Chemical or toxic compound exposures: Benzene, asbestos, nickel, cadmium, vinyl chloride, benzidine, N-nitrosamines, tobacco or cigarette smoke, asbestos, and aflatoxin
  • Ionizing radiation: Uranium, radon, ultraviolet rays from sunlight, radiation from alpha, beta, gamma, and X-ray-emitting sources
  • Pathogens: Human papillomavirus (HPV), EBV or Epstein-Barr virus, hepatitis viruses B and C, Kaposi's sarcoma associated herpes virus (KSHV), Merkel cell polyomavirus, Schistosoma spp., and Helicobacter pylori
  • Genetics: A number of specific cancers have been linked to human genes. These include breast, ovarian, colorectal, prostate, skin and melanoma

Risk factor of Cancer:

All most everyone has risk factors for cancer and is exposed to cancer causing substances such as sunlight, secondary cigarette smoke, and X-rays during their lifetime, but many individuals do not develop cancer. In addition, many people have the genes that are linked to cancer but do not develop it. The higher the amount or level of cancer causing materials a person is exposed to, the higher the chance the person will develop cancer. In addition, the people with genetic links to cancer may not develop it. This may be due to lack of enough stimulus to make the genes function or they may have a strong immune response that controls or eliminates cells that are or potentially may become cancer cells. Even certain dietary lifestyles may play a significant role in conjunction with the immune system to allow or prevent cancer cell survival. For these reasons, it is difficult to figure out a specific cause of cancer for many individuals.
Other risk factors that may increase cancer risk are:

  • processed meats (salted, smoked, preserved, and/or cured meats)
  • barbecued meat, due to compounds formed at high temperatures
  • obesity
  • lack of exercise
  • chronic inflammation
  • hormones, especially those hormones used for replacement therapy

cell phones, caffeine and pickled vegetables have very minimal risk of developing cancer.

Symptoms of Cancer:

Symptoms of cancer depend on the type of cancer, where it is located and where the cancer cells have spread. For example, there will be a lump in the breast or nipple discharge in case of breast cancer. Metastatic breast cancer may present with symptoms of pain if it has spread to bones, extreme fatigue if spread to lungs, or seizures if spread to brain). In few cases there won't be any  signs or symptoms until the cancer is advanced.
The warning signs and symptoms that would indicate the presence of a cancer and should require medical attention are:

  • Change in bowel or bladder habits
  • A sore throat that does not heal
  • Chronic indigestion or difficulty swallowing
  • Nagging cough or hoarseness
  • Unusual bleeding or discharge (for example, nipple secretions or a sore that will not heal that oozes material)
  • Thickening or lump in the breast, testicles, or elsewhere
  • Obvious change in the size, color, shape, or thickness of a wart or mole

Other signs or symptoms that would indicate other form of cancer are:

  • Unexplained loss of weight or loss of appetite
  • Persistent fatigue, nausea, or vomiting
  • A new type of pain in the bones or other parts of the body that may be steadily worsening. The pain may come and go, but is unlike previous pains one has had before
  • Unexplained low grade fevers which may be either persistent or come and go
  • Recurring infections which will not clear with usual treatment

These symptoms may also arise from noncancerous conditions. Therefore it is important to diagnose the condition correctly. There are also presence of specific symptoms for the different cancer types. For example, lung cancer may present with common symptoms of pain which is usually located in the chest. There may be unusual bleeding, that usually occurs when the patient coughs. Fatigue and shortness of breath are more common symptoms for lung cancer.

Types of cancer:

There are more then 200 types of cancer. Some of the general type of cancers are:


Cancer that begins in the skin or in tissues that line or cover internal organs. Example include: skin, lung, colon, pancreatic, ovarian cancers, epithelial, squamous and basal cell carcinomas, melanomas, papillomas, and adenomas


Cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Example include: bone, soft tissue cancers, osteosarcoma, synovial sarcoma, liposarcoma, angiosarcoma, rhabdosarcoma, and fibrosarcoma


Cancer that starts in blood forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood. Example include: lymphoblastic leukemias (ALL and CLL), myelogenous leukemias (AML and CML), T-cell leukemia, and hairy-cell leukemia

Lymphoma and myeloma:

Cancers that begin in the cells of the immune system. Example include: T-cell lymphomas, B-cell lymphomas, Hodgkin lymphomas, non-Hodgkin lymphoma, and lymphoproliferative lymphomas

Central nervous system cancers:

Cancers that begin in the tissues of the brain and spinal cord. These are called brain and spinal cord tumors. Example include gliomas, meningiomas, pituitary adenomas, vestibular schwannomas, primary CNS lymphomas, and primitive neuroectodermal tumors.
Metastatic cancer cells are not listed in the general category as they arise from one of the cell type listed above. The major difference from the above types is that these cells are now present in a tissue from which the cancer cells did not originally develop. The tissue from which the cancer cells arose should be included in metastatic cancer. More accurate statement is metastatic breast, lung, colon, or other type cancer with spread to the organ in which it has been found.
Prostate cancer that has spread to bones are called as metastatic prostate cancer to bone. This is not same as bone cancer, which would be cancer that started in the bone cells. Metastatic prostate cancer to bone is treated differently than lung cancer to bone.

Staging of Cancer:

Different staging methods are used for cancers and the specific staging criteria varies among cancer types. Most staging systems depends on

  • Location of the primary tumor
  • Tumor size and number of tumors
  • Lymph node involvement, that is spread of cancer into lymph nodes
  • Cell type and tumor grade that means how closely the cancer cells resemble normal tissue cells
  • The presence or absence of metastasis

The two main methods that form the basis for the more specific or individual cancer type staging are TMN and stage grouping method. The TMN staging is used for most solid tumors while the Roman numeral or stage grouping method is used by some clinicians and researchers on almost all cancer types.
The TNM system is based on three factors. These include:

  • the extent of the tumor (T)
  • the extent of spread to the lymph nodes (N)
  • the presence of distant metastasis (M)

Depending on the size or extent of the primary tumor and the extent of cancer spread, a number is added to each letter . Higher number indicates bigger tumor or more spread.
The following is how the NCI describes the TNM staging system:

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 these are not cancer, CIS may become cancer and is sometimes called pre-invasive 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, that means number of lymph nodes and/or extent of spread

Distant metastasis (M):

MX : Distant metastasis cannot be evaluated (some clinicians do not ever use this designation)
M0 : No distant metastasis
M1 : Distant metastasis is present
Based on this, cancer of a person could be listed. For example, T1N2M0, means it is a small tumor (T1), but has spread to some regional lymph nodes (N2), and has no distant metastasis (M0).
The Roman numeral or stage grouping method is described by the NCI as follows:

  • Stage 0: Carcinoma in situ.
  • Stage I: 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 II: The cancer has spread to another organ(s).   
  • Stage III: The cancer has spread to another organ(s).   
  • Stage IV: The cancer has spread to another organ(s).

There are also variations of these staging methods. Some cancer registries use surveillance, epidemiology, and end results program (SEER) termed summary staging. SEER groups cancer categorize the cancer 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.
Staging of cancer is very important. It helps the physician to
  • decide on the most effective treatment protocols, provide a basis for estimating the prognosis for the patient
  • provides a system to communicate the condition of a patient to other health professionals that become involved with the patients' care.

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