Breast cancer is probably the most frequent and fatal neoplasm in women of the western world, and it causes more fear, suffering and morbidity than any other disease in our times. It is also one of the most costly diseases not only in "lost earnings" but also in terms of physical and psychic energy spent and skills used for the many aspects of its care. Furthermore, the incidence of this tumor is slowly but steadily increasing while our means of treating it remain ineffec tive in distressingly many patients. Breast cancer thus represents an increasing threat to public health. The clinician responsible for the management of patients with this distressing disease has found himself, in recent years more than ever before, in a very awkward state of uncertainty. Many of his tradi tional views or practices have been questioned. The new concepts challenging his position are based on evidence at times so esoteric that, being often unable to comprehend it, he may subconsciously tend to distrust it. To his further dismay, clinicians and investigators of equal caliber and repute in this field disagree so widely and on so many important issues that he can no longer refer to an authoritative source for guidance; his horizons are therefore blurred and the stage is set for confusion. Much of what underlies the current controversy stems from our ignorance concerning the etiology of breast cancer and our inability to comprehend the many eccentricities of its clinical behavior.