Cancer screening
The term screening is commonly used for a test that is used for evaluation of a person for possible disease without the person ever having any symptoms or signs of the disease. Screening tests are usually undertaken in a target population, which has significantly high risk of developing the disease. Mammogram is a screening technique used for breast cancer, and the target population for mammogram is women who are aged 40 and above. PSA testing is a screening test for prostate cancer and the target population is men over 50 years of age. Screening tests cannot be employed in all diseases. In some cases a useful screening test may not be available, and in some other cases it may not be worth screening for a disease because screening and finding out the disease early may not change the natural history of disease. The later is probably true in case of screening of lung cancer. From the studies so far published, there is no clear evidence to suggest that screening for lung cancer in high-risk population (smokers) would improve survival.

Breast cancer screening
Unlike lung cancer, breast cancer can be screened using available techniques with beneficial results. Mammogram is the only accepted screening test for breast cancer. Mammogram till this date may have saved lives of thousands of women, by detecting the disease at a very early stage, when it is mostly curable. Screening for mammogram does not prevent the occurrence of breast cancer, but instead it provides a very simple and useful technique to detect breast cancer at a very early stage. Mammogram is capable of detecting breast cancer at a stage prior to infiltration of the tumor to the surrounding structures, called stage 0 breast cancer or carcinoma in situ. Recommendations for breast cancer screening vary from country to country and within the same country according to the views of different organizations who recommend the screening. American Cancer Society recommends that "women age 40 and older should have a screening mammogram every year and should continue to do so for as long as they are in good health."

What is a mammogram?
Mammogram is just an X-ray photograph of your breast, and works in principle the same way as your chest X-ray. The breast tissue is compressed between two plates and an X-ray picture is taken. Doctors would look at the X-ray and determine if there are any abnormalities in the picture. Breast cancer usually appears in the form of calcifications, architectural distortions, or abnormal densities. Since mammogram uses X-rays, there may be slight risk associated with exposure to radiation in women who get mammograms. However the amount of radiation associated with mammogram examination is very small and is strictly controlled by regulatory agencies like National Department of Health and Human Services. Very strict regulations are enforced by this agency to make sure that mammography equipment is safe and uses the lowest dose of radiation possible. The dose of radiation used by the modern mammogram machines does not significantly increase the risk of breast cancer.

Digital mammography
Digital mammograms are similar to conventional X-ray film mammograms except that the pictures are produced in the digital media in a computer. Digital pictures have the advantages of manipulation of light and contrast and hence would be more useful for the studying the mammography picture. It was claimed in the past that digital mammogram is superior to conventional mammograms in terms of accuracy, however a recent study has shown that digital mammography no better than regular mammography.

Computer Aided Detection (CAD)
CAD is sophisticated computer program that can compare areas of the digital mammography picture and aid the physician to more easily detect breast cancer. Studies have shown that CAD system improved diagnostic accuracy by about 20 percent.

Clinical breast examination and self breast examination
An article on breast cancer screening will not be complete without mentioning clinical breast examination and (CBE) and self breast examination (SBE). CBE and SBE are useful adjuvant to mammogram for detection of breast cancer. It is also to be mentioned that about 10 percent of all tumors that can be felt by the physicians may not be seen in a mammogram, hence if the physician feels a tumor, the absence of abnormality in the mammogram does not ensure absence of a breast tumor. Such patients should be evaluated by biopsy.

Self-breast examination as the name implies denotes examination of breast by women, without the help of a physician. This can be undertaken in the privacy of their home. Probably the best time to do a self-breast examination is while taking showers. Women can ask their physicians to teach them the technique of self-breast examination. American Cancer Society recommends "women in 20s and 30s should have a clinical breast examination (CBE) as part of a periodic (regular) health exam by a health professional preferably every 3 years. After age 40, women should have a breast exam by a health professional every year." Regarding self-breast examination, American Cancer Society gives the following recommendations: "BSE is an option for women starting in their 20s. Women should be told about the benefits and limitations of BSE. Women should report any breast changes to their health professional right away."