WHY MAMMOGRAPHY IS NOT PERFECT

By Caroline A. Reich, MD, PhD

Women’s Imaging Associates

Birmingham, Alabama

Without a doubt, mammography is the most sensitive screening test developed for the early detection of breast cancer. Many lives have been saved because cancers have been caught when they are small and treatment is most likely to lead to a cure. However, like any screening test, the sensitivity (the ability to detect cancer) is not perfect. Some studies suggest that up to 20% of breast cancers may not be detected on mammography.

Several factors limit the sensitivity of mammography. First, not all breast cancers are the same. Some cancers like Ductal Carcinoma in Situ (DCIS) are often detected because of tiny, irregular calcifications that are deposited within the tumor and then seen on the mammographic images. Other cancers such as Invasive Ductal Carcinoma often cause distortion within the tissue, showing up as a mass with irregular margins.  Invasive Lobular Carcinoma is a particularly aggressive cancer that may grow quite large before distorting the normal tissue enough to be visible.

Just as breast cancers differ, the density of each woman’s breast tissue is variable and is a factor that can affect the sensitivity of the exam. Normal breast tissue ranges from being primarily fatty in composition to dense with fibroglandular elements. The density of the breast parenchyma will affect the appearance of the mammogram. A breast that is composed primarily of fat will be gray on the mammogram. A breast with dense tissue will be much whiter. Unfortunately, the signs of malignancy such as calcifications and tissue distortion are also white and can be obscured at times by the white tissue in a dense breast.

What can you do to increase your chances of detecting breast cancer as early as possible?

     1.       Most importantly, get a yearly mammogram once you turn forty! While mammography is not perfect, it remains the best screening tool we have, even in dense breasts. Tiny, irregular calcifications are a common sign of cancer. These suspicious calcifications are usually invisible on ultrasound or breast MRI.

      2.       Do NOT skip monthly breast self-exams! There are some cancers that are apparent as a breast lump before being visible on mammography. 

      3.       Know your breast density. Every mammography report includes a statement describing the relative density of the breast tissue. If you have dense breasts and have an increased risk for breast cancer such as a mother, sister or daughter with breast cancer, discuss with your healthcare provider your options for additional screening with breast ultrasound.