It is the first time that an issue has been devoted to the work of a single individual. An Editorial Board member since the inception of the journal in 1989, Alfred G. Knudson this year celebrates his 80th birthday, and a number of friends and colleagues have expressed the wish to honor this outstanding scientist in this way. Given the central importance of the "two-hit" hypothesis to the evolution of our understanding of genes, chromosomes, and cancer, this recognition is certainly appropriate.
Al's very thoughtful analysis of the pattern of inheritance of retinoblastoma led to the development of a new paradigm, the validity of which is still apparent more than 30 years later. The inheritance of a mutant allele of a critical gene as a predisposing factor for the development of a malignant cell is recognized in ever more human cancers. It was Al's observations that led us on the correct path.
This issue includes commentaries from Al's many friends, students, and colleagues, as well as those whose research has been influenced by his hypothesis. We join his many admirers in celebrating him and his remarkable scientific contributions.