A mammogram is a screening test for breast cancer that basically provides an x-ray of the breast. The breast is compressed between two plates to spread the tissue and allow better detection of possible tumors. Densely packed areas of breast tissue, including tumors, appear as bright white spots on the film. While mammograms are a very useful screening tool, they have known limitations and an abnormal result does not always mean breast cancer.
Limitations
Women younger than 50 years of age tend to have breast tissue with more ligaments and glands that can complicate the interpretation of mammograms, since both normal dense breast tissue and tumors appear as white areas on the film. Mammograms are more accurate for older women.
The Mayo Clinic says that tiny metallic particles in common lotions and deodorants can produce odd results on a mammogram and reminds women not to use these products on the day of their test.
Accuracy
According to the National Cancer Institute, most abnormal findings on a mammogram turn out not to be breast cancer. These "false positive" findings occur more often in younger women; those taking hormones, especially estrogen or progesterone, as in birth control pills; women who have had a breast biopsy in the past; and women with a family history of breast cancer.
Abnormal Results
Calcium deposits are usually benign, due to normal aging, injury to the breast or a non-cancerous tumor, but very small and irregularly distributed deposits could indicate cancer. New spots of dense tissue since a previous mammogram can indicate cancer. Areas of distorted tissue hint at the presence of a tumor.
Tumor Risk
The National Cancer Institute points out that some of the tumors found on mammograms, even if ultimately proven to be cancerous, might have never caused symptoms. Unfortunately, as of 2010, there is no way to know in advance of further tests which cancerous tumors pose a risk and which do not. However, the National Cancer Institute adds that breast cancers found by mammography in women over the age of 65 usually are not life-threatening.
Follow-Up
The Mayo Clinic says that approximately 10 percent of all mammogram tests produce results that show a potential problem and require follow-up tests. Before further testing, an abnormal finding on a mammogram should be compared to the woman's previous mammograms to be sure the finding is actually suspicious. A repeat mammogram or an MRI of the breast might give a better indication if the area is actually a tumor. In some cases, a doctor might suggest a biopsy to check the actual tissue for cancer cells.
