Mammograms are special x-rays of the breast that can identify breast cancer before a woman or her doctor can feel a lump. Mammograms are not totally accurate. They sometimes suggest cancer when it is not present (a false-positive result), or look normal even though cancer is present (a false-negative result). Younger women's breasts contain less fat and are denser than older women's breasts. Also, if women take hormones, such as progestin and estrogen, their breasts become less fatty and denser. Mammograms of dense breasts are harder to read than mammograms of fatty breasts. Women with dense breasts may need additional imaging studies to confirm the presence of lesions or cancer. Few studies have assessed ways to reduce the number of “recalls” for additional testing when breasts are dense and mammogram findings are unclear.