Risk of second cancer after cancer in childhood.

Against the background of a seemingly short latency period for the majority of childhood tumors and the theory of the existence of a prezygotic variation of the two-step mutation model prior to tumor development, the risk of second cancer after cancer in childhood is examined in the population of Denmark from 1943-1980. A total of 5319 cases of primary cancer in childhood were followed until patient death or the end of 1980, and the number of secondary tumors were observed, specifying on diagnosis, age, sex, and time since first tumor diagnosis. A total of 23 secondary tumors was observed (O) against an expected (E) figure of 6.5, corresponding to an O/E ratio of 4.4. The risk varies greatly according to time elapsed since first diagnosis, with the highest risk in close relation to the primary tumor. The second tumor is probably more frequently localized to the skin and brain than elsewhere, and the risk of a second tumor is particularly associated with leukemia and osteosarcoma in childhood. It is concluded that the results are compatible with the theory of a prezygotic variation of the two-step mutation model.