For nearly two thousand years, since Galen's observation in the second century that cancer accompanied melancholic personalities, observers have likened personality, or aspects of personality, to malignancy. The difficulty, in terms of the kind of hard scientific proof that is considered desirable, is the fact that most of these observations are ex post facto. Until very recently, few prospective studies have been done. Those that do exist, as well as all the many retrospective studies and observations, confirm a predisposing set of personality factors, attitudes, and beliefs.

Steven Locke and Mady Hornig-Rohan have edited a recent comprehensive annotated bibliography linking immune competence with the mind. Mind and Immunity: Behavioral Immunology contains 1304 articles and nearly 150 books, book chapters, and review articles dealing with the relationship of mind and immunity. In it, forty-nine papers on the topic of Personality and Cancer are cited. Most of these support a relationship between cancer and personality factors, with the predominant factor being depression and the helplessness/hopelessness syndrome. In many studies significant loss, in childhood or shortly predating the onset of illness or both, was also found.

One of the most interesting, and conclusive, evidences of the effect of personality on physiology comes from recent studies of people with multiple personalities. People with multiple personalities, like those made well known in books and movies such as The Three Faces of Eve and Sybil, have always created interest because of their strange switches in behavioral characteristics. The changes in behavior have included different body language, sometimes accents, speech mannerisms, handwriting, hobbies and skills, and different phobias and memories.

New interest is being generated by the fact that these people not only change behavior, but their brains and their bodies also change. Different personalities within one person have different brain wave patterns, different handedness, and different allergies. Eyeglass prescriptions and such objective measures as eye pressure and corneal curvature differ. A person may be nearsighted or farsighted in different personalities or even be colorblind in one but not another. As they change from personality to personality, these people experience dramatic physical characteristic changes as well.

Bennett Braun, a Chicago psychiatrist who has studied a number of persons with multiple personality disorder, notes that these changes in physiology are not greater than those that can be achieved through hypnosis. And this implies, in turn, at least theoretically, that there are no changes achieved through hypnosis that could not also be achieved through voluntary control. After all, the hypnotist holds no strings within the body of his subject. The person with multiple personality is controlling all the changes in physiology made, albeit unconsciously. Conscious control of the unconscious can be learned, perhaps of any system over time and surely over any system that can be affected by personality shifts or by hypnosis.

Early in their work connected with the psychological management of malignancy, Carl and Stephanie Simonton compiled an annotated bibliography. They reviewed the medical literature concerned with the etiology of cancer, and in more than two hundred articles they found a relationship between personality factors, emotional factors, and cancer. They found the most prevalent predisposing condition to be the loss of an important love object or relationship six to eighteen months prior to the diagnosis of malignancy. According to the authors, these losses create hopelessness because they recapitulate lack of closeness, loss, or rejection experienced in childhood. The most common personality characteristics they found were a tendency to hold resentments, difficulty in forgiving others, a tendency toward self-pity, poor ability to develop and maintain long-term relationships, a poor self-image, and feelings of rejection in general.