Decreased rate of DNA-chain growth in human basal cell carcinoma

The DNA synthetic (S) phase of cell division is about twice as long in human basal cell carcinoma (BCC) as the normal epidermis and several non-malignant skin diseases. A similar increase in S phase duration seems to occur in tumours of the human oesophagus, larynx and recto-colon. At the molecular level, the overall rate of replication in a nucleus is determined by two factors--the frequency of initiation of replication and the rate of replication fork progression along the units of replication (for review see refs 7,8). Here we present evidence (based on DNA fibre autoradiography) that the observed increase in S phase duration may be due to a marked reduction in the rate of DNA replication along replication units, the density of simultaneously operating replication units remaining unchanged. This indicates an alteration in some biological component(s) of DNA synthesis in BCC that is of potential interest for characterizing the malignant transformation of the epidermal cell and that may perhaps be exploited therapeutically.