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A total of 491 cases of breast cancer were reviewed to evaluate the diagnostic importance of the three standard projections; craniocaudal, mediolateral, and oblique. With only one projection, 90% of the malignancies would have been detected; with two and three projections the percentages rose to 94% and 95%, respectively. Nonvisualization was due to either juxtathoracic position of the tumor or superimposition of dense tissues. A relation was found between the position of a juxtathoracic tumor and the projection in which it was visualized. The mean diameter of tumors not visible due to superimposition of dense tissues was smaller than that of the whole material. In breast screening programs, use of two projections, the oblique and craniocaudal, is recommended.
Andersson et al. (1978) studied this question.