Cancers are capable of spreading through the body by two mechanisms: invasion and metastasis. Invasion refers to the direct migration and penetration by cancer cells into neighboring tissues. Metastasis refers to the ability of cancer cells to penetrate into lymphatic and blood vessels, circulate through the bloodstream, and then invade normal tissues elsewhere in the body.

Tumors (Neoplasms)

The gradual increase in the number of dividing cells creates a growing mass of tissue called a "tumor" or "neoplasm." If the rate of cell division is relatively rapid, and no "suicide" signals are in place to trigger cell death, the tumor will grow quickly; if the cells divide more slowly, tumor growth will be slower. But regardless of the growth rate, tumors ultimately increase in size because new cells are being produced in greater numbers than needed. As more and more of these dividing cells accumulate, the normal organization of the tissue gradually becomes disrupted.

Malignant versus Benign Tumors

Depending on whether or not they can spread by invasion and metastasis, tumors are classified as being either benign or malignant. Benign tumors are tumors that cannot spread by invasion or metastasis; hence they only grow locally. Malignant tumors are tumors that are capable of spreading by invasion and metastasis. By definition, the term "cancer" applies only to malignant tumors.

Why Cancer Is Potentially Dangerous

A malignant tumor, a "cancer," is a more serious health problem than a benign tumor because cancer cells can spread to distant parts of the body. For example, a melanoma (a cancer of pigmented cells) arising in the skin can have cells that enter the bloodstream and spread to distant organs such as the liver or brain. Cancer cells in the liver would be called metastatic melanoma, not liver cancer. Metastases share the name of the original ("primary") tumor. Melanoma cells growing in the brain or liver can disrupt the functions of these vital organs and so are potentially life threatening.

Cancer Detection and Diagnosis

Detecting cancer early can affect the outcome of the disease for some cancers. When cancer is found, a doctor will determine what type it is and how fast it is growing. He or she will also determine whether cancer cells have invaded nearby health tissue or spread (metastasized) to other parts of the body. In some cases, finding cancer early may decrease a person's risk of dying from the cancer. For this reason, improving our methods for early detection is a high priority for cancer researchers.

Early Cancer May Not Have Any Symptoms

Don't wait to feel pain before getting checked for cancer because cancer does not always have symptoms. Some people visit the doctor only when they notice changes like a lump in the breast or unusual bleeding or discharge. However, early cancer may not have any symptoms. That is why screening for some cancers can help, particularly as you get older. Screening methods are designed to check for cancer in people with no symptoms.

Pap Test

A screening technique called the Pap test (or Pap smear) allows early detection of cancer of the uterine cervix. In this procedure, a doctor uses a small brush or wooden scraper to remove a sample of cells from the cervix and upper vagina. The cells are placed on a slide and sent to a laboratory, where a microscope is used to check for abnormalities.

Mammograms

Breast cancer can sometimes be detected in its early stages using a mammogram, an X-ray of the breast. Mammography is most beneficial for women as they age and undergo menopause.  Mammography is a screening tool that can detect the possible presence of an abnormal tissue mass. By itself, it is not accurate enough to provide definitive proof for either the presence or absence of breast cancer.  If a mammogram indicates the presence of an abnormality, further tests must be done to determine whether breast cancer actually is present.

Blood Tests

Many cancers cannot yet be readily detected in their early stages, but scientists are working hard to find new clues. Scientists are trying to develop blood tests that might alert people to such cancers while they are still in their early stages. For example, several blood tests for ovarian or prostate cancer are under active study.

One example is a substance called prostate-specific antigen (PSA), produced by cells of the prostate gland. PSA circulates in the blood and can be detected and measured with a simple blood test.

Fecal Occult Blood Test (FOBT)

A procedure called a fecal occult blood test (FOBT) detects invisible amounts of blood in the feces, a possible sign of several disorders, including colon cancer. The test is painless and can be done at home or in the doctor's office. With an application stick, a dab of a stool specimen is smeared on a chemically treated card, which is tested in a laboratory for evidence of blood. If blood is confirmed in the stool, more tests may be performed to find the source of the bleeding. Early detection using FOBT may help to decrease mortality from colon cancer.