The Human Yolk Sac and Yolk Sac Tumors

I am honored to have been invited to write a foreword for this book, because tumors of the yolk sac have been a preoccupation of mine since the days of my residency, now more than 3 decades ago. At that time, a 3-year-old boy died of a testicular cancer of unknown histo­ genesis. It was bad enough that the child died, but it bothered me even more that medical science did not know the histogenesis of the tumor that destroyed him, and I decided to study testicular cancer. For re­ search training