Mammography does a good job of detecting calcifications that may be cancerous. However, some noncalcified masses — which are more common in dense breast tissue — also can be cancerous, and these are harder to detect with mammography. More than half of women younger than 50 years old and about a third of those 50 and older have dense breasts, and mammographic sensitivity for this group is estimated to be as low as 30 to 48 percent.

Dr. Wendie A. Berg from American Radiology Services Inc., Johns Hopkins at Green Spring Station in Lutherville, Md., and her colleagues recently investigated how well the combination of mammography and ultrasound detects breast cancer compared with mammography alone in women who have an elevated risk.

As reported in the May 14 issue of JAMA, 2637 women with an elevated risk of breast cancer underwent both mammography and ultrasound in randomized order. The interpreting radiologist for each examination was blinded to the results of the other.

Forty women (41 breasts) were diagnosed with cancer. Eight were suspicious on both mammography and ultrasound, 12 on mammography alone and 12 on ultrasound alone. Nine cancers (eight women) were not detected by either.

The results indicated that mammography alone yields about 7.6 cancers per 1000 women screened, and combined ultrasound and mammography increases the yield to 11.8 per 1000 screened. The researchers concluded that adding ultrasound to mammography increases the cancer detection yield by 4.2 cancers per 1000 women who are at an increased risk of breast cancer. However, they caution that ultrasound also increases the number of false positives.