Radiation induced malignancies are considered a risk of radiation treatment. How much of this is fact and how much is fiction?
While this is an accepted fact, the real risk of skin cancer induced by radiation treatment is low. Studies of children receiving radiation therapy for ringworm found relative risk of 3.6 primarily for BCCa of the head and neck among irradiated Caucasian children. Doses ranged from 3 Gy to 6 Gy to the scalp. In the studies, significantly increased risks for skin cancer were noted for basal cell cancers only. Additional exposure to UV irradiation was required to manifest the increased risk. Although similar increase was seen with benign skin tumors, malignant melanoma was not increased. The estimated relative risk was 0.7 per Gy. The minimum latency was 20 years after exposure. Up to 50 years of follow-up was shown.
Although, caution must be used in choosing radiation treatment for skin cancers, in patients 65 and older the risks appear to be small.
Unlike skin cancer, radiation-induced leukemia generally occurs within 3 to 5 years of radiation exposure, solid tumors usually start to be diagnosed a minimum of 10 to 15 years after exposure.
What appears to be fiction is transformation of existing skin cancers into more aggressive variants with radiation. In a setting of polyclonal cancer cellular populations, if there is a presence of radioresistant population of cells within the cancer, then by simple selection, these will be the cells that will survive radiation therapy. As such, these cell lines will continue to grow after treatment with radiation therapy. This, of course, is not the same thing as inducing less malignant carcinomas to transform into more malignant variants. Without radiation, the same aggressive cell lines would be present and would continue to grow regardless. As such, the belief that radiation induces a more aggressive transformation of an existing cancer is fallacious.