Breast cancer is one of the two most common cancers diagnosed in women. Early detection is the key to survival. Screening mammography is often the first test to detect a breast cancer and can do so at the very earliest stages.

What is a Mammogram?

A mammogram is an x-ray of the breast as it is being compressed between two plates. It is classified as a non-invasive procedure; however, it does involve variable amounts of pain during compression. The breast is exposed to very low doses of ionizing radiation with this procedure as two images of each breast are taken. One of these is taken with the breast being compressed from top to bottom, called craniocaudal (CC). The other is taken with the breast being compressed side to side, looking from the central to the lateral part of the breast, called medial-lateral oblique (MLO). When oriented correctly, a physician puts these two images side by side and is able to determine where a mass or suspicious area is in the three dimensional breast.

Newer technology such as digital mammogram and computer-aided systems are beginning to be used at some institutions. Full-field digital mammography, or FFDM, replaces the standard x-ray film with solid state detectors, similar to those in a digital camera. These detectors convert electrical signals into an image that is displayed on a computer screen, where they can be closely examined and printed if necessary.[1] Computer-aided detection (CAD) is a system that evaluates digital or standard mammogram images for suspicious lesions.[2] The program is especially designed to detect calcifications and areas that are denser than others that could represent a mass. CAD detects a potential abnormality but a radiologist must use clinical judgment to determine whether or not cancer is or could be present.

Who Needs a Mammogram?

The National Cancer Institute has set guidelines that help determine who needs a mammogram and how often they are needed.[3]

  • Women age 40 and above should have a mammogram every one to two years
  • Women that have a higher risk secondary to family history should discuss with their doctor whether or not they should have a mammogram sooner than 40 years old.
  • Some suggest that women should have a baseline mammogram between the ages of 35-40, as having a normal mammogram to compare to is helpful.

The American College of Obstetricians and Gynecologists has also issued screening guidelines for breast cancer. They recommend a woman has a mammogram screening every year beginning at age 40. They based this recommendation on three findings:[4]

  • Breast cancer being diagnosed in increasingly younger women
  • The lag time of cancer development (the time between the initial appearance of breast cancer and when it is detectable by mammogram)
  • The potential to decrease mortality from breast cancer in this age group, as has been shown in women older than 50 years old that have regular screening

Screening and Diagnostic Mammograms

All mammograms are not created equal. A screening mammogram is what most people are referring to when they talk about mammograms, and is described above. Diagnostic mammograms are similar to screening mammograms and are done when a screening mammogram detects a suspicious area but the breast tissue is too dense to evaluate properly. During this procedure, the breast is compressed even more so, spreading the tissue thinner and making it easier to characterize the suspicious area.

How Does It Work?

As mentioned, a mammogram uses low-dose x-rays to create an image of the internal anatomy of the breast. The x-rays pass through tissue and is absorbed in variable degrees depending on density. Bone, which is very dense, appears bright white because it absorbs more radiation than soft tissues such as fat, muscle and solid organs, which appear as various shades grey.

Mammography is an outpatient procedure performed by a radiology technician. The technician will:

  • Assist you in placing your breast on a platform that will compress it during the exam
  • Slowly allow the machine to compress your breast, taking the x-ray when fully compressed
  • Change the position of the machine to take the two views mentioned above
  • Do this for both breasts

The images are created by the technician but they do not interpret them. This can be frustrating for some women, especially if there is reason to believe that they may have cancer. The mammogram images are read by a radiologist, who is a physician that has been trained to read them. The results are typically available within one week

The Pros and Cons of Mammography

As with every procedure, mammograms have pros and cons. Let’s take a look at some of them.[5]



Relatively non-invasive and can be performed in an outpatient setting Uses radiation, which is a risk factor for cancer development
Can detect breast cancer in situ, which is pre-invasive Fails to detect all breast cancers
Can detect small or large tumors False positive rate of 5-15%, where a suspicious finding turns out to be normal

Regular screening for breast cancer is important and mammography is a very effective screening modality. Access to mammography can sometimes limit a woman’s ability to participate in regular screening.[6]


1  Mammography. (2011). Retrieved from Radiology

2 Ibid

Mammograms. (n.d.). Retrieved from National Cancer Institute:

4  New Guidance Issued for Breast Screening. (2011). Contraceptive Technology Update. American College of Obstetricians.

5  Mammography, op. cit.

6 Somkin, Carol P., Stephen J. McPhee, Tung Nguyen, Susan Stewart, Sarah J. Shema, Bang Nguyen and Rena Pasick. (September 2004) The Effect of Access and Satisfaction on Regular Mammogram and Papanicolaou Test Screening in a Multiethnic Population. Med Care 42(9): 914-926.

This article was originally published on July 27,2012 and last revision and update of it was 9/2/2015.