A standard two-view mammogram and specialized views, including magnified images, can provide vital information, but mammography is not a definitive diagnostic test since 10 to 15 percent of cancers are not detectable by this technique. A suspicious palpable mass should be biopsied even if mammography does not show cancer.
• Mammograms may detect an abnormality elsewhere in the same or opposite breast. These images may show
  microcalcifications suspicious for cancer (even if no mass is palpable) or a smaller, non-palpable but still 
  suspicious mass. In this situation, a biopsy must be done, usually guided by mammography, to determine 
  whether the lesion is cancer.
• Mammography may also be used to evaluate women with precancerous breast conditions, to evaluate yearly 
  the opposite breast of women with known breast cancer (as there is a higher risk of developing cancer there) 
  and to evaluate women with metastatic adenocarcinoma from an unknown primary source. Sometimes the 
  primary source is a hidden breast cancer. This last point is especially important because breast cancer may 
  respond to chemotherapy or hormonal therapy not used to treat other forms of metastatic cancer.
• Ultrasound evaluation (breast ultrasonography) may be used to diagnose cysts. The accuracy of
  ultrasonography in determining whether a mass is cystic (containing fluid) or solid approaches 100 percent.
  This may eliminate the need for more complex procedures. Some physicians prefer to withdraw fluid from all 
  cysts with a simple needle and syringe (aspiration). If clear fluid is removed and the mass completely 
  disappears, no further treatment or evaluation is needed.