Tumor location and detectability in mammographic screening

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Abstract
The adequacy of a film mammogram that does not visualize the retromammary space or ribs has concerned radiologists. The 79 prevalent cancers detected in the 10,000 self-referred woman at the University of Michigan Breast Cancer Detection Demonstration Project were analyzed for number of films required to detect the cancer, relationship of the cancer to the posterior edge of the film, number of occult lesions, tumor size, histologic type, sensitivity of detection method, and number of interval carcinomas. The mammograms were obtained using a dedicated mammographic machine and the upright position, with visualization of the anterior axillary fold on the mediolateral view. The ribs were not imaged. Of the 79 cancers, 76 were detectable on the mammogram. All were visualized on the mediolateral view, while three were not imaged on the craniocaudal view. Twelve percent of the cancers were within 1 cm of the posterior edge of the film. Only six "interval" carcinomas were found in the 10,000 patients within the year of the initial examinations; these women had dense P2 or DY mammographic parenchymal patterns. The detected cancers were smaller and had a significantly higher percentage of noninvasive cancers than in a symptomatic clinical population. Thus, properly exposed film mammograms using vigorous breast compression examine the breast adequately without visualizing the ribs.