The different effects of apoptosis and DNA repair on tumorigenesis.

Complex multicellular organisms have evolved mechanisms to ensure that individual cells follow their proper developmental and somatic programs. Tumorigenesis, or uncontrolled cellular proliferation, is caused by somatic mutations to those genetic constraints that normally operate within a tissue. Genes involved in DNA repair and apoptosis are particularly instrumental in safeguarding cells against tumorigenesis. In this paper, we introduce a stochastic framework to analyse the somatic evolution of cancer initiation. Within this model, we study how apoptosis and DNA repair can maintain the transient stability of somatic cells and delay the onset of cancer. Focusing on individual cell lineages, we calculate the waiting time before tumorigenesis in the presence of varying degrees of apoptosis and DNA repair. We find that the loss of DNA repair or the loss of apoptosis both hasten tumorigenesis, but in characteristically different ways. Copyright 2002 Elsevier Science Ltd.