Not all mutations produce a cancer cell since they may not occur in key oncogenes or tumor supressor genes. More than one mutation is necessary to produce a cancer cell. Spontaneous mutations are unlikely by themselves to cause the initiation and progression events that lead to cancers. Radiation Radiation as a mutagen can be compared with chemical carcinogenesis and several points can be found in common. This damage induces DNA repair processes which is prone to error and may lead to mutations.
Fixation appears to be complete after the first postirradiation mitotic cycle.
A promotion phase is required for full expression of the initiated malignant alteration. Nucleic acid bases acquire excited energy states and produce photochemical reactions between DNA bases when cells are exposed to UV light. The principal products in DNA are cyclobutane dimers formed between two adjacent pyrimidine bases in the DNA chain. That formation of these dimers is linked to mutagenic events. Mutants defective in repair of cyclobutane pyrimidine dimers have increased sensitivity to the lethal and mutagenic effects of UV light.