The definitive diagnosis of cancer is usually based on microscopic examination of tissue or cell samples by a pathologist. This diagnosis serves as a guide to the choice of treatment that, in at least some instances, may lead to the cure of the disease. The increasing sophistication in the classification of some cancers, such as malignant lymphomas and certain tumors of childhood, has led to quasi-specific treatment modes that match the disease process with optimal therapy, often with felicitous results.
Unfortunately this group of cancers comprises only a small fraction of all malignant tumors when compared with the common carcinomas of various organs. Despite some progress, no established sophisticated methods of classification exist today for most carcinomas beyond histological tumor typing and grading and clinical staging. The success of treatment of these tumors varies enormously: it is common knowledge that small cancers, preferably still confined to the site of origin,