Use and abuse of mammography in the early diagnosis of breast cancer.

In the 8 years before 1980, 3958 women were examined in the St. Michael's Hospital breast clinic in Toronto. Of 302 women with breast cancer, 87 (29%) had normal mammograms. Breast cancer was found in 34 after at least one clinical and mammographic examination had given normal results. Of these, 6 (18%) cancers were detected only by mammography while, paradoxically, 23 (68%) were detected only by clinical examination. Normal mammograms are significantly (p less than 0.001) more frequent in young women with breast cancer and in those with small palpable breast cancers. Mammography is most productive when used as a routine study in older women who have clinically normal breasts. All women should start having them around the age of 40 to 45 years. How often they should be repeated is debatable. There is no evidence that they should be repeated annually. Under 35 years of age mammography for any reason is unrewarding. Biopsy of a breast lump that is solid on aspiration should never be delayed because of a normal mammogram. Biopsy of a radiologically suspicious lesion in the breast should never be delayed because the findings on clinical examination are normal.