Increased incidence of tongue cancer after primary radiotherapy for nasopharyngeal carcinoma - the possibility of radiation carcinogenesis

The aim of this study was to define the risk of tongue and other aerodigest ive tract cancers developing after primary radiation therapy for nasopharyn geal carcinoma (NPC). A cohort of 903 patients with non-disseminated NPC gi ven radical radiotherapy between 1984 and 1989 was studied for the incidenc e of tongue cancer and other malignancies during follow-up. A contemporary cohort of 87 patients with tongue cancer, without a history of NPC, was stu died for demographic data, cigarette smoking and alcohol consumption habits . These were then compared with all the NPC patients and with the NPC patie nts who later developed tongue cancers. There was a significantly increased number of tongue cancers following radiotherapy for NPC. The risk of devel oping tongue cancer after radiotherapy for NPC was 0.13% per patient per ye ar. There was no increase in the number of other malignancies. The associat ion between NPC and tongue cancer was that of a non-random temporal sequenc e with tongue cancers following NPC but not in the reverse order. The demog raphic data and smoking and alcohol consumption history of the 7 NPC patien ts who subsequently developed tongue cancer were significantly different fr om the de novo tongue cancer patient population. The absence of common aeti ological factors between NPC and tongue cancer and the non-random sequence of tongue cancers occurring after NPC suggests that these seven tongue canc ers could be radiation induced. The estimated radiation dose received by th e part of the tongue developing cancer was substantial and significantly hi gher than the dose to the cancer-free tongue. An increase of tongue cancers after radiotherapy for NPC is reported and arguments are made in support o f the hypothesis that these were radiation-induced malignancies. We suggest a decrease in the volume of tongue included within the planning target vol ume of NPC in the absence of oropharyngeal and/or parapharyngeal infiltrati on. Awareness of the association should make early diagnosis of this likely radiation-induced cancer possible. (C) 1999 Elsevier Science Ltd. All righ ts reserved.