In the absence of prevention, the control of breast cancer demands that it be discovered as soon as possible after it reaches threshold size, but before it disseminates. This optimal detection time is known as the "cancer control window." The actual doubling time of a cancer is a major determinant of the length of time available for effective discovery. Data are presented showing the enormous variance possible for this interval, ranging from very short times to extremely long times. With refined mammographic techniques and conscientious, aggressive mammographers, this threshold size continues to shrink and now approaches 2 mm. Many factors, however, continue to influence effective detection in this size range including cancer type, breast parenchymal density, proper applications of examination techniques, and the duration of the cancer control window for different cancers. Our own experience and review of the literature indicate that a certain percentage of cancers will be missed in the symptomatic and screened populations. With some adjustments of technique and interpretation and careful attention to them, many of these overlooked cancers can be recognized. However, data support the presence of a subset of acute breast cancers below threshold size at examination but that can grow to clinically detectable and symptomatic size within weeks to months of the breast evaluation showing no abnormality. These cancers will surface under any contemporarily available screening or detection program through no physician error. Under optimal conditions, this group of cancers can neither be prevented nor recognized and account for the inability of the radiologist to diagnose some breast cancers.