[Second primitive malignant neoplasm after radiotherapy]

Since the prolongation of survival for patients treated by radiotherapy second primary cancers are not rare. Cumulative incidence of second primary malignancy after radiotherapy (SPMAR) 40 years after treatment can reach 20 % when patients were 40 years old at treatment time. Among SPMAR some of them can be promoted by irradiation. Relative risk (RR) analysis is the most common method used to estimate the proportion of such second cancers. Most of studies reported a RR around 1.1 in adult patients. In young patients RR is about 6, meaning that SPMAR attributable to irradiation is more elevated in this subgroup. Quantification of these events, biomolecular mechanisms, risk factors are complex and not yet fully understood. Information given to patients must be adapted and the cost/benefit ratio has to be justified regarding SPMAR risk. Irradiation technique optimisation is an important point especially in young patient and adults, in order to reduce at maximum the volume of organ at risk exposed while not compromising optimal dose given to the tumour volume, although no standard rules of irradiation are definitively established at the present time.