As scientists learn more about the structure and function of cancerous cells, they are able to develop new methods for both treatment and screening. There are several important reasons to screen healthy people for cancer. The most obvious is to catch cancer early, when it is easier to treat. However, in the long term, cancer screening can also help to decrease the number of people who develop cancer, and the number of people who die from cancer or its complications. The ultimate goal is to eliminate deaths from cancer completely.

Although screening for cancer has many benefits, it also carries some risk. False positive or negative results may lead to too little or too much treatment, or unnecessary treatment, as in the case of slow-growing cancers that would not have caused any harm during the person's life. One of the best ways to determine whether a screening method is actually useful for early diagnosis, prevention, or lowering the incidence of cancer/cancer deaths is to study the screening methods in controlled, randomized clinical trials.

Screening recommendations

Because different organizations may recommend slightly different screening regimens, it is best to discuss cancer screening with your doctor. Below are some recommendations from the American Cancer Society (ACS):

Breast cancer

Mammography. An X-ray of the breast.

• Women 40 and older should have one every year

Clinical breast examination. A breast examination performed by a medical professional.

• Women age 20 to 40 should have one every three years; women 40 and older should have one every year

Breast self-examination. A breast examination performed by women on their own breasts.

• Women age 20 and older should perform one each month; the examination is considered "optional"

Cervical cancer

Pap test. Cells are gently scraped from the outside of a woman's cervix and vagina and examined.

• Women should have a Pap test beginning three years after becoming sexually active or beginning at age 21
• A standard Pap test should be done each year, or a liquid pap test can be done every two years

Pelvic exam. A doctor examines a woman's vagina, cervix, uterus, fallopian tubes, ovaries, and (sometimes) the rectum.

• Women age 18 to 40 should have one every one to three years; women 40 and older should have one every year

Colorectal cancer

The ACS recommends screening for colorectal cancer beginning at age 50 for both men and women using one of the tests mentioned below. Common screening tests include:

Colonoscopy. This test checks the upper and lower part of the colon with a thin, lighted tube. The ACS recommends that men and women 50 and older should have one every 10 years.

Digital rectal exam. In this test, a doctor inserts a gloved finger into the rectum to feel for anything abnormal. The ACS does not have recommendations for this test.

Fecal occult blood test (FOBT). This test is used to detect hidden blood in stool (feces). The ACS recommends that men and women 50 and older should have one every year.

Flexible sigmoidoscopy. This test checks the lower part of the colon with a thin, lighted tube. The ACS recommends that men and women 50 and older should have one every five years, preferably with a FOBT.

Prostate cancer

Prostate-specific antigen (PSA) test. This blood test measures the level of a marker called PSA that may detect early prostate cancer. However, high PSA levels may also indicate conditions that are not cancer.

• Men 50 and older should be offered testing every year

Skin cancer

Complete skin examination. A doctor checks the skin for signs of skin cancer.

• Men and women should have skin examinations done periodically