Radiation dose and relapse are predictors for development of second malignant solid tumors after cancer in childhood and adolescence: A population-based case-control study in the five Nordic countries

The aim of the study was to assess the risk with radiation therapy and chemotherapy of the first cancer in childhood and adolescence for the development of a second malignant solid tumor (SMST). Also, the role of relapse of the primary tumor was studied. It is a nested case-control study within a Nordic cohort of patients less than 20 years of age at first diagnosis 1960 - 1987. SMSTs were diagnosed in 1960-1991. There were 196 cases and 567 controls. The risk was increased only for radiotherapy given more than five years before the development of the SMST. A significantly increased relative risk of 1.8 was found already at doses below 1 Gy. The risk increased rapidly up to a maximum of 18.3 for doses above 30 Gy. Chemotherapy alone did not increase the risk to develop an SMST. However, in combination with radiotherapy, chemotherapy showed a significant potentiating effect. Relapse was found to be an independent risk factor for development of an SMST, with a higher relative risk for females than for males.