A mammogram is a special x-ray of the breasts used to diagnose abnormalities, including breast cancer. It is the single most effective way to detect cancer in its early stages, when it is most treatable. Mammography can find abnormalities between one and three years before they can be felt. When breast cancer is detected before it has spread to the lymph nodes, patients have a five-year survival rate of 98 percent, according to the American Cancer Society (ACS). Only one or two mammograms out of every 1,000 leads to a diagnosis of cancer.

Mammograms detect cancer by revealing tissues that are denser than those in the normal tissues of the breast. They can detect lesions as small as 0.5 centimeters (0.2 inches). Most lumps cannot be felt until they are at least 1 centimeter (0.4 inches). 

Mammograms can detect calcium deposits in the breast. Appearing as small, white dots on film, these can be the result of cell secretions, cell debris, inflammation, trauma, previous radiation or foreign bodies. Calcium deposits that are tiny and irregularly shaped (microcalcifications) are often associated with cancer. They may appear alone or in clusters. When found, they may prompt a follow-up mammogram or a biopsy. Microcalcifications are the most common sign on a mammogram of ductal carcinoma in situ (early noninvasive cancer confined to the breast ducts).

Larger, coarser deposits called macrocalcifications are sometimes the result of a benign (noncancerous) condition called fibroadenoma. This is a common tumor of the female breast. Aging of the breast arteries, old injuries and inflammation are also common causes of macrocalcification. Macrocalcifications are not cancerous and are found in half of women over age 50 and in one in 10 women under 50, according to the ACS.

Masses or lumps can occur with or without calcifications. While they are sometimes cancerous, they are often cysts (a noncancerous collection of fluid) or benign tumors, such as fibroadenomas. The presence of a cyst needs to be confirmed with either a fine needle aspiration or a breast ultrasound. Suspected cancerous masses usually require a biopsy for confirmation. As with calcifications, masses can be caused by benign breast conditions or by breast cancer. The size, shape and edges (margins) of the mass help the physician determine whether or not it is cancer. The physician will also look for:

• Dense areas that appear in only one breast
  
  
• Dense areas or microcalcifications that were not seen in the patient’s last mammogram
  
  
• Distorted areas (which may suggest tumors that have invaded nearby tissues)

Sometimes, dense areas in mammograms indicate tissue packed with glands that make calcifications and masses harder to detect. On the other hand, dense areas may also indicate cancer itself.

If suspicious areas are found, a physician may order an ultrasound or needle aspiration to help determine whether the mass is solid (such as in a tumor) or is a fluid-filled cyst. If nipple discharge is present, a physician may order an x-ray exam called galactography, a procedure in which a fine plastic tube is placed into the opening of the nipple’s duct and a contrast material is injected into the duct.

Patients may obtain mammograms from many different facilities, including hospitals, clinics, physicians’ offices and x-ray or imaging centers. Mobile units also provide mammograms during screening events at shopping malls, community centers and offices. A federal law called the Mammography Quality Standards Act (MQSA) regulates mammography. Under MQSA, all mammography personnel and facilities, including mobile units, in the United States must be accredited and be certified by the Food and Drug Administration (FDA). In addition, these facilities must pass annual inspections and display their FDA certificate in a location visible to patients.

Although mammograms are the most effective way to screen for breast cancer, studies have shown that many women fail to get them regularly. Common reasons provided by women included fear, embarrassment and most often, cost. Mammogram costs vary according to a patient's insurance coverage. Medicaid and private insurance typically cover the full cost of an annual screening mammogram on women over 40. However, Medicare only covers 80 percent of the cost, forcing women to pay the remaining 20 percent. Many states offer mammograms at low or no cost to women who qualify based on income.

The ACS recommends that women age 40 and older have a mammogram every year, while the National Cancer Institute (NCI) recommends mammograms every one to two years for this age and risk group. Women younger than 40 may be advised to get mammograms if they have other risk factors for breast cancer.

Women at higher risk of breast cancer should consult their physician about when to begin scheduling mammograms, and how often to have the procedure. Risk factors that may increase the scheduling of mammograms include:

• Personal history of breast cancer
  
  
• Breast cancer in mother or sister
  
  
• Family history or personal history of gene abnormalities associated with cancer (e.g., BRCA1 or BRCA2 genes)
  
  
• No pregnancies or first pregnancy after age 35
  
  
• Early onset of menstruation
  
  
• Late menopause
  
  
• History of atypical findings or prior breast biopsies
  
  
• Treatment with radiation therapy to the chest or neck before age 30

Mammograms are most effective when used to examine the breasts of women over age 40. As a woman ages, breast tissue increasingly is replaced with fat. By the time a woman reaches menopause, there are usually just a few strands of breast tissue left. Fat appears gray on mammograms, making it easy to see the white spots that indicate abnormalities. In contrast, the breasts of younger women are usually too dense to provide good mammogram images.

Mammogram rates have decreased in the past several years, especially among groups of women with previously high screening rates, according to the American Cancer Society (ACS). Experts are concerned about the decline, especially because it coincides with a decline in breast cancer rates. Although some of the decline in cases may be attributed to better and earlier screening, some cases may be undetected because women are not getting screening mammograms.

In many cases, an ultrasound or magnetic resonance imaging (MRI) is a good substitute for women in the older age group. MRI in conjunction with a mammogram also may be recommended for women who are at high risk for the disease. The ACS recommends women in their 20s and 30s have a clinical breast exam by a health professional every three years.