CLSPN and cancer: In the initial phases of oncogenesis, Claspin may have to be silenced because Claspin activation in response to DNA damage would promote Chk1 activation, which in early oncogenesis, would inhibit cancer development through the prevention of genome instability (an enabling feature of cancer) in a dosage-dependent manner, and the accumulation of the genetic mutations required for cancer promotion (Figure 2, top) [1,110,111].