The position of "Cancer Teaching Coordinator" at The University of Chicago has been a consistently rewarding one because of the enthusiasm and support of the faculty and the students. This volume is the result of the second of two recent intensive teach­ ing sessions which have been planned and implemented by the group which forms the Cancer Coordinator's Advisory Committee. The first of these teaching sessions was held in early March of 1964 and was entitled "LEUKEMIA, A Current and Forward Look. " It attracted overflow attendance from the students and staff of this medical institution augmented by members of the other medical centers in Chicago. It was a stimulating and instructive colloquium, and the only regret we heard expressed afterward was that we had not arranged for publication of the many excellent presentations. One of the events commemorating the seventy-fifth anniversary of the founding of The University of Chicago was this symposium on malignant transformations. This time the Committee advised us to plan on speedy publication, and, logically, it chose Dr. Werner Kirsten, a member of our faculty and an active and effective investigator in this general field of endeavor, to serve as editor of the volume. Again, two of the same ingredients for effective instruction were blended: an excellent group of scientists presenting their latest work and a fine, attentive audience of students and staff.