One method of attacking the problem of high cancer mortality, the second foremost cause of death, has been education of lay and medical persons to recognize the symptoms suggestive of early cancer. Periodic health examinations have also been advocated as a method of detecting early tumors, again with some success. At the same time the treatment of cancer has been improved, especially in external and accessible types, by refinements in surgery and irradiation. Ideas as to what constitute surgical accessibility have undergone gradual change, so that today every major area in the body is surgically accessible. The posterior mediastinum was one of the last to yield. Tumors may, however, still be inoperable and incurable because of their extent.
These methods attack the problem of symptomatic cancer—cancers which have symptoms. They leave untouched the important field of presymptomatic cancer, or cancer which is as yet symptomless, silent, latent or preclinical. Apparently