Mammography and ultrasound in the diagnosis of contralateral breast cancer.

Forty-nine (5%) of 956 women referred for follow-up imaging after breast cancer treatment had a malignancy in both breasts. The mammograms and ultrasonograms or US reports, and histologic slides or pathologic reports of 31 of these patients were reviewed. Mammography was more sensitive than clinical examination or US in detecting contralateral breast cancer, the sensitivity of mammography being 81%. Thirty-nine percent of the contralateral cancers were nonpalpable, and all were first detected at mammography. No cancers were depicted by US alone. US provided complementary information about palpable masses in 50% of the cases in which the mammographic finding was difficult to interpret. The mammographic appearance and the difficulties in detecting a contralateral cancer were similar to those known to be characteristic for first primaries. Distinguishing a new primary from a metastasis from the first breast cancer was not always possible by means of mammography or US.