Cancer Basics – Causes, Signs and symptoms

Cancer Basics

Reviewed By:
Martin E. Liebling, M.D., FACP
Mark Oren, M.D., FACP


Cancer is a disease in which abnormal malignant body cells uncontrollably grow and multiply. There are many different forms of cancer including carcinomas, sarcomas, lymphomas, leukemias and myeloma.

The body normally regulates the growth, division and death of its cells. When cancer develops, this normal regulation is disrupted and cancer cells continue to grow and divide uncontrollably, forming new abnormal cells. Although some cancers grow rapidly, others do not. The continued, inappropriate growth and lack of normally programmed cell death make a growth malignant. This process creates a mass of tissue known as a tumor or neoplasm. Frequently, cancer cells spread or metastasize from the initial tumor to nearby tissues or organs. Cancer also may spread to distant areas of the body via the bloodstream or the lymphatic system. Although cancer typically forms a tumor, not all tumors are cancerous (malignant). Those tumors that are not malignant are classified as benign. In addition, some cancers, such as leukemia, involve the blood and do not form solid tumors.

Cancer can develop almost anywhere in the body. According to the American Cancer Society (ACS), people in the United States are most often diagnosed with skin cancer (non-melanoma), prostate cancer, breast cancer, lung cancer and colorectal cancer.

Symptoms of cancer vary depending on where it develops and where it has spread in the body. General signs and symptoms include fatigue, unexplained weight changes, fever, pain, or a lump that seems to be growing. However, cancer may not produce any symptoms in its early stages.

According to the ACS, cancer is the second leading cause of death in the United States. However, millions of people are living with cancer or have had the disease. More than 1 million people develop cancer each year, according to the ACS. About one out of every two men and one out of every three women will develop some type of cancer at some point during their lifetime. Although anyone can develop cancer, it is more common in certain age groups and ethnic populations.

About cancer

Cancer is a disease in which the cells in part of a person’s body grow uncontrollably. Although there a many different types of cancer, they all develop as a result of uncontrolled growth of abnormal malignant cells.

Normally, cells grow, divide and die in an orderly way. The rates of new cell growth and old cell death are kept in balance. In a healthy person, the cells divide at a rate to repair injuries and to replace depleted or dying cells, while the old and damaged cells self-destruct in a process known as apoptosis.

This normal balance is disrupted during the development of cancer. Cancer cells continue to grow and divide uncontrollably, outliving normal cells and continuing to form new abnormal cells. This increase in cell division generates a growing mass of tissue known as a tumor or neoplasm. As new cells are being produced in greater numbers than needed by the body, the tumor will increase in size. The growth rate of a tumor depends on the rate of cell division. When cells divide rapidly, the tumor will grow quickly and vice versa.

Typically, cancer forms as a tumor. However, not all tumors are malignant. Noncancerous or benign tumors do not spread and are normally not life threatening. Some types of cancer do not involve tumor masses in one place, but are diffused throughout the body. An example is the leukemias, which involve the blood and blood-forming organs.

Frequently, cancer cells travel from the initial tumor to other areas of the body where they begin to grow and replace healthy tissue. There are two main terms used to describe the spread of cancer from its original location:

  • Invasion. Cancer cells invade neighboring tissues. For example, invasive cancer cells in the breast may penetrate into tissues within or near the breast.

  • Metastasis. Cancer spreads beyond the immediate neighboring area to other body areas. It may penetrate the lymph vessels and blood vessels, enter the bloodstream and invade normal tissue in adjacent and distant areas of the body. The likelihood that cancer will metastasize depends on the type of cancer and its stage. Although each patient’s case is unique, some types of cancer have a tendency to spread to certain areas, including the lungs, bones and brain.


Cancer can develop almost anywhere in the body. Although it may spread to other parts of the body, it is always named for the area where it originated. For example, melanoma (cancer of the cells that produce skin coloring) that spreads to the liver is classified as metastatic melanoma, not liver cancer.

According to the American Cancer Society (ACS), approximately one out of every two men and one out of every three women will develop some type of cancer at some point during their lifetime. Although cancer is the second leading cause of death in the United States, millions of people are living with cancer or have had cancer. The National Cancer Institute estimates that 10.5 million Americans with a history of cancer were alive in January 2003.

More than one million people develop cancer each year, according to the ACS. Although anyone can develop cancer, it is more common in certain age groups and ethnic populations. Approximately 77 percent of all cancers are diagnosed in people age 55 and older, and the rate of occurrence (incidence rate) varies among ethnic groups. According to the ACS, the cancers most commonly diagnosed in the United States include:

Type of cancerPredicted new
cases in 2007
Skin cancer (non-melanoma)More than 1,000,000
Prostate cancer218,890
Lung cancer213,380
Breast cancer180,510
Colorectal cancers (colon/rectum)153,760 (112,340/41,420)
Bladder cancer 67,160
Non-Hodgkin’s lymphoma63,190
Skin cancer (melanoma)59,940
Kidney cancer(renal cell and renal pelvis)51,190
Endometrial cancer39,080
Pancreatic cancer37,170
Thyroid cancer33,550

Types and differences of cancer

Cancer can develop almost anywhere in the body, and there are many different forms of cancer. The main forms of cancer include:  

  • Carcinomas. Develop from the cells that cover external and internal body surfaces. These are the most common type of cancer. The most common carcinomas to occur in the United States include lung cancer, breast cancer, prostate cancer and colon cancer.
  • Sarcomas. Develop from cells found in the supporting tissues of the body such as the bone, cartilage, fat, connective tissue and muscle.

  • Lymphomas. Develop in the lymph nodes and the tissues of the immune system.

  • Leukemias. Develop in the immature blood cells that grow in the bone marrow and accumulate in the bloodstream.

  • Myeloma. Develops in the plasma cells of the bone marrow, which normally make gamma globulin, an important immune system defense. 

In order to distinguish among different types of carcinomas, sarcomas, myelomas, lymphomas and leukemias, scientists use a variety of technical names. Usually the names are created by using Latin prefixes that stand for the location where the cancer began. Cancer prefixes include:

Erythro-Red blood cells
Hemangio-Blood vessels
Melano-Pigment cell
Myelo-Nonlymphocytic bone marrow

Using this system, cancer arising from the bone is known as osteosarcoma and cancer of glandular cells is known as adenocarcinoma, such as adenocarcinoma of the breast or prostate.

Potential causes of cancer

Cancer cells develop as a result of damage to deoxyribonucleic acid (DNA). Located in every cell, DNA is the molecule that directs all cell activities including growth, division and function. Usually the body is able to repair DNA when it is damaged. However, in cancer cells damaged DNA may not be repaired normally.

Damaged DNA can be inherited from a parent, or more commonly, normal DNA can become damaged by environmental factors. Chemicals, radiation, viruses and heredity all play a role in the development of cancer by producing changes, or mutations in DNA. In some cases, DNA mutations occur for no apparent reason.

Genes are made of the chemical bases that form DNA. They contain information that determines an individual’s outward appearance, including hair color, eye color and height. They also contribute to an individual’s risk of developing certain diseases, such as some types of cancer. Genes are carried on chromosomes. Normally, humans have 23 pairs of chromosomes. In each pair, one member is inherited from the person’s father, and the other member is inherited from the person’s mother. Each chromosome contains many genes, hundreds or thousands for some chromosomes.

Mutations can be seen in many types of genes. However, the following types of genes are most often associated with cancer-linked mutations:

  • Oncogenes. Genes that promote cell division. Oncogenes develop from the mutation of normal genes (proto-oncogenes). Proto-oncogenes instruct cells to produce proteins involved in growth control. While oncogenes also perform this function, they order a distorted version or excessive amounts of the proteins. As a result, the presence of an oncogene causes a cell to continually grow and divide.

    The presence of oncogenes in certain forms and/or overactivity can trigger the development of cancer. In healthy cells, oncogenes can contribute to cancer development by ordering cells to produce proteins that encourage excessive cell growth and division.

  • Tumor suppressor genes. Genes that instruct cells to manufacture proteins responsible for slowing cell growth and division. The absence of tumor suppressor genes has been linked to cancer development.

    The p53 gene is a particular type of tumor suppressor gene that produces a protein that causes apoptosis, or cell suicide, which is a normal occurrence. When the DNA in a cell is damaged, the p53 protein normally stops cell growth and division. When the DNA damage cannot be repaired, the p53 protein will initiate apoptosis, thus preventing the damaged cell from growing uncontrollably.

    Cancer may develop when a pair of tumor suppressor genes are either lost from a cell or inactivated by mutation. Such an absence would cause cells to uncontrollably grow and divide.    

    People who inherit an increased risk of developing cancer are frequently born with one defective copy of a tumor suppressor gene. Because genes come in pairs, an inherited defect in one copy will not lead to cancer because there is another normally functioning copy. Cancer may develop only when the second copy undergoes mutation, and the patient no longer has a normally functioning copy of the gene.

  • DNA repair genes. Genes that instruct cells to produce proteins required to correct errors that may occur when cells duplicate their DNA prior to division. When these genes become mutated they can fail to repair, allowing additional mutations to build up.

Usually multiple mutations must occur for cancer to develop. It may develop as the result of an accumulation of mutations involving oncogenes, tumor suppressor genes and DNA repair genes. Cancer can begin with a defect in one type of gene, such as a tumor suppressor gene, that allows excessive cell production. The cells often acquire additional mutations involving DNA repair genes, other tumor suppressor genes and several other growth related genes. Eventually the accumulating mutations can produce a highly malignant (cancerous) tumor that is able to metastasize (spread).

Genes can be mutated in several ways. Researchers have identified a number of DNA mutations that “turn on” oncogenes and “turn off” tumor suppressor genes, thereby causing cancer to develop. These include:

  • Translocations. The transfer of DNA from one chromosome to another.

  • Deletions. The loss of part of a chromosome.

  • Inversions. The rearrangement of DNA in part of a chromosome.

  • Additions. All or part of a chromosome is duplicated and too many copies are found in a cell.

Although these mutations have been identified and connected with cancer, researchers are still unaware of exactly how the mutations happen and why they occur in some people but not in others. While causes are unknown, certain factors have been found to increase the risk of cancer, including tobacco and alcohol use, excessive exposure to ultraviolet rays and unhealthy diet.

Signs and symptoms of cancer

Cancer can cause a variety of signs and symptoms. The type of sign or symptom depends on the size of the cancer, the location of the cancer, how much it is affecting neighboring organs and other body parts, and whether it has spread (metastasized). Many of the signs and symptoms associated with cancer may also be caused by noncancerous conditions.

As cancer grows, it begins to affect nearby organs, blood vessels and nerves. When these areas are compromised, numerous  body parts are pushed or their normal function is compromised, it may create a variety of signs and symptoms. Cancer may also cause generalized or nonspecific signs and symptoms. These may be caused by immune system reactions or by cancer cells releasing substances that alter the body’s metabolism.

General signs and symptoms of cancer include:

  • Fatigue. Fatigue is the most common symptom experienced by patients diagnosed with cancer. It typically occurs as a patient’s cancer progresses. In some patients, however, it may develop earlier. This commonly occurs with cancers that cause chronic blood loss, including some colon or stomach cancers, or as a side effect of cancer treatments.

  • Unexplained weight changes. Most people with cancer will lose weight at some point. In some patients, an unexplained weight loss of 10 pounds (4.5 kilograms) may be the first sign of cancer. It is especially common in patients with stomach cancer, lung cancer, esophagus cancer and pancreatic cancer, although in some cases, the cancer clearly causes decreased food intake. Some cancer patients will also experience unexplained weight gain in response to hormones secreted by tumors in the body.
  • Fever. Fever may be an early sign of some cancers, such as Hodgkin’s lymphoma. Although it occurs often in patients with cancer, fever is more common in the advanced stages of the disease. It may develop when cancer or cancer treatment affects the immune system and reduces the body’s resistance to infection. 
  • Pain. Pain usually develops during the advanced stages of cancer. However, it may occur early in bone cancer or testicular cancer.

  • Skin changes. Skin cancer, as well as other types of cancer can cause a variety of changes in the skin. Common skin changes include:
    • Hyperpigmentation (darkening of the skin)
    • Jaundice (yellowing of the skin)
    • Erythema (reddening of the skin)
    • Itching
    • Excessive hair growth

Other common signs and symptoms include:

  • Changes in bladder or bowel function. Cancer can cause a variety of changes in bladder and bowel function including:
    • Chronic constipation
    • Diarrhea
    • Blood in urine or stool
    • Change in the size of stool
    • Painful urination
    • More frequent or less frequent urination

      These changes may indicate colon cancer, bladder cancer, prostate cancer or a variety of other noncancerous conditions.
  • Sores that do not heal. Cancer can cause sores in a variety of areas including the skin, mouth, penis or vagina. Sores in these areas may indicate skin cancer, oral cancer, penile cancer or vulvar cancer among other conditions.

  • Unusual bleeding or discharge. Cancer can cause a variety of bleeding disorders including:
    • Blood in the phlegm
    • Blood in the stool
    • Blood in the urine
    • Unusual vaginal bleeding
    • Bloody discharge from the nipple
    • Unusual bleeding or discharge can occur in the early or advanced stages of cancer. It can be a sign of lung cancer, colon cancer, rectal cancer, cervical cancer, endometrial cancer, bladder cancer, kidney cancer, breast cancer and a variety of other conditions.

  • Lump or thickening. Many types of cancer can be felt as thickening or a lump through the skin. Often these skin changes are detectable in the breast, testicle, lymph nodes and soft tissues of the body. Patients may benefit from performing monthly breast or testicular self-examinations.

  • Indigestion or dysphagia (difficulty swallowing). These symptoms may indicate a variety of conditions, including esophageal cancer, stomach cancer and pharyngeal cancer.

  • Changes in a wart or mole. Certain changes in a wart or mole may indicate melanoma, including a change in color, shape or size. In addition, if the border of a lesion becomes less definite, it may be a sign of cancer. 

  • Persistent cough or hoarseness. These symptoms may indicate a variety of conditions including lung cancer, thyroid cancer and laryngeal cancer.

Early symptoms of cancer, such as fatigue, may be overlooked because they may resemble symptoms of more common illnesses or have an obvious cause. In other cases, the patient may choose to ignore the symptoms because they are frightened. Patients are encouraged to contact their physician when they experience any symptom of cancer. This is particularly important when symptoms have been present for a considerable amount of time, such as weeks, or become worse. The earlier cancer is diagnosed, the better the patient’s chance for successful treatment. Cancer-directed physical examination may also help make a diagnosis earlier but many cancers cause no symptoms in their early stages.

Questions for your doctor regarding cancer

Preparing questions in advance can help patients have more meaningful discussions with their physicians about their conditions. Patients may wish to ask their doctors the following questions related to cancer:

  1. What cancers am I most at risk of developing?
  2. What are the most common signs of these cancers?
  3. What tests will be used to diagnose my suspected cancer?
  4. Will I need a biopsy to tell the type and stage of the cancer?
  5. What types of specialists will I need for my cancer?
  6. What are the treatment options for this type of cancer?
  7. What lifestyle changes can I make to reduce my risk of cancer?
  8. What type of monitoring will I need after cancer treatment?
  9. Does this cancer put me at risk for other types of cancer?
  10. Are my children at greater risk for cancer based on my diagnosis?
  11. Should we undergo genetic testing?
  12. How will my prognosis be determined?
  13. Can you recommend a cancer support group?
  14. What resources are available for me to learn about this cancer?
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