A mammogram is an x-ray of the breast. Mammography can find a lump as much as 2 years before it can be felt.
Cancers that are found on mammograms but that cannot be felt (nonpalpable cancers) are smaller than cancers that can be felt, and they may not have spread. The vast majority of cancers that are too small to be felt and have not spread are curable.
On the other hand, mammography is not foolproof. Some breast changes, including lumps that can be felt, do not show up on a mammogram. Changes can be especially difficult to spot in the dense, glandular breasts of younger women. This is why women of all ages should have their breasts examined every year by a physician.
Mammography is a simple procedure. The standard screening exam includes two views of each breast, one from above and one angled from the side. A registered technologist positions the breast between two flat plastic plates. The two plates are then pressed together. The idea is to flatten the breast as much as possible; spreading the tissue out makes any abnormal details easier to spot with a minimum of radiation. The technologist steps from the room and takes the x-ray, then returns and repeats the procedure for the next view.
The pressure from the plates can be uncomfortable, or even slightly painful. It helps to remember that each x-ray takes just a few moments-and that it could save your life. It also helps to schedule mammography just after your period, when your breasts are least likely to be tender.
Although some women are concerned about radiation exposure, the risk of any harm is extremely small. First of all, the doses of radiation used for mammography are very low. Specialized mammography facilities have experienced personnel as well as modern equipment that is custom-designed for mammograms. The combination of good technology and expertise makes it possible to obtain good quality x-ray images with very low doses of radiation. (See "More Info: Choosing a Mammography Facility.")
Women should be further reassured to know that any effect of radiation on the breasts decreases sharply with age. Studies of women exposed to large doses of radiation in years past (for instance, in the course of treatment for tuberculosis) show that breast cancer developed more commonly only among those who had been young-often in their early teens-at the time they received the radiation.
The exact amount of radiation needed for a specific mammogram will depend on several factors. For instance, breasts that are large or dense will require higher doses to get a clear image. Federal mammography guidelines limit the radiation used for two views of one breast to 1 rad. (A "rad" is a unit of measurement that stands for radiation absorbed dose.) In practice, most mammograms deliver just a small fraction of this amount.