Radiation-associated and 'spontaneous' human thyroid carcinomas show a different pattern of ras oncogene mutation.

Activated ras oncogenes in experimentally induced rodent tumours have been demonstrated to show specific patterns of oncogene activation which depend on the inducing agent, with H-ras activation in nitrosomethylurea (NMU) induced tumours, and K-ras activation in tumours induced by ionising radiation. We report a study of 12 radiation-associated human thyroid tumours, using polymerase chain reaction (PCR) amplification of paraffin-embedded material and allele-specific hybridisation with mutant-specific probes for the 3 ras oncogenes. Compared to 68 'spontaneous' human thyroid tumours, the radiation-associated cases show the same overall prevalence of ras mutation. However there is a significantly higher rate of K-ras mutation in radiation-associated follicular carcinomas than in 'spontaneous' follicular carcinomas (60% compared to 6%, P less than 0.05), suggesting that radiation may preferentially activate K-ras in human as well as rodent tumours.