Second malignant neoplasms after a first cancer in childhood: temporal pattern of risk according to type of treatment

The variation in the risk of solid second malignant neoplasms (SMN) with ti me since first cancer during childhood has been previously reported. Howeve r, no study has been performed that controls for the distribution of radiat ion dose and the aggressiveness of past chemotherapy, which could be respon sible for the observed temporal variation of the risk. The purpose of this study was to investigate the influence of the treatment on the long-term pa ttern of the incidence of solid SMN after a first cancer in childhood. We s tudied a cohort of 4400 patients from eight centres in France and the UK, P atients had to be alive 3 years or more after a first cancer treated before the age of 17 years and before the end of 1985. For each patient in the co hort, the complete clinical, chemotherapy and radiotherapy history was reco rded. For each patient who had received external radiotherapy, the dose of radiation received by 151 sites of the body were estimated. After a mean fo llow-up of 15 years, 113 children developed a solid SMN, compared to 12.3 e xpected from general population rates. A similar distribution pattern was o bserved among the 1045 patients treated with radiotherapy alone and the 206 4 patients treated with radiotherapy plus chemotherapy; the relative risk, but not the excess absolute risk, of solid SMN decreased with time after fi rst treatment; the excess absolute risk increased during a period of at lea st 30 years after the first cancer. This pattern remained after controlling for chemotherapy and for the average dose of radiation to the major sites of SMN. It also remained when excluding patients with a first cancer type o r an associated syndrome known to predispose to SMN. When compared with rad iotherapy alone, the addition of chemotherapy increases the risk of solid S MN after a first cancer in childhood, but does not significantly modify the variation of this risk during the time after the first cancer.