Recognition of the imperative need for the detection of cancers in their early stages has resulted in directing attention in the last decade or so to the asymptomatic, presumably healthy adult. Efforts have been directed toward developing techniques by which a relatively standard clinical and laboratory examination of the apparently well adult would identify those persons harboring silent (and presumably "early" and curable) cancer. This is true cancer detection. The vital role of the individual physician, heeding and investigating even the most minimal of symptoms and performing at periodic intervals a routine complete physical examination with special reference to key sites, has been epitomized in the slogan "Every doctor's office a cancer detection center."

The natural course of most cancer includes a stage during which it is localized within a single organ. In the earliest phase the disease consists of a microscopic lesion confined to the tissue of origin. This in situ stage of cancer may persist for a long period of time before either local invasion or distant metastasis takes place. In the case of the cervix uteri, where intraepithelial carcinoma has been most extensively studied, it has been demonstrated that the preinvasive stage may persist for many years. Similar in situ lesions have been identified in the breast and in the respiratory, gastrointestinal, and genitourinary tracts. It is probable that all cancers originating in a single tissue or organ pass through such a primary focal stage.

It follows that cancer confined to a single organ which can be removed by surgery or to a tissue which can be destroyed by radiotherapy or other means is curable cancer if detected at that stage, and the problem of cancer cure does, in fact, resolve itself into one of increasing the practice of early diagnosis.

In recent years a number of investigators have taken the position that cancer pursues an inexorable and predetermined course, influenced little or not at all by attempts at control and treatment. This course is said to be dictated by the inherent, indefinable, and unpredictable "biologic" nature of the individual tumor. According to these workers, it is of little use to find the "early case" since the prognosis is completely unpredictable and independent of size or type of tumor, stage of disease, presence or absence of symptoms, delay in diagnosis and treatment, or treatment itself. This despairing philosophy of the nature and natural history of cancer is unquestionably applicable in certain specific instances. At one end of the spectrum there are minute but aggressive cancers, ideally treated, which pursue a relentless course to death. At the other extreme are the large and bulky but indolent lesions, subjected to every error or delay in treatment, which permit long survival. Unquestionably, these examples occur and are typical of a small percentage of cancers which exhibit a natural history independent of all clinical management. However, in the middle of the spectrum, wherein lies a substantial majority of cancers, all these factors of type, size, stage, speed of management, and treatment are important and decisive. It is this precept which underlies efforts directed toward the detection and early diagnosis of cancer.