Double primary malignant tumors and history of therapeutic irradiation to initial primary malignant tumor

During an 18-year period from April 1959 to December 1977, 4,186 patients with malignant tumors were treated by radiation at the Department of Radiology, Gunma University, School of Medicine. Of these patients, 67 (1.6%) were diagnosed as double primary malignant tumor at the clinic. These patients were divided into four groups according to the history of radiation therapy to initial primary malignant tumor (IPMT). Group I: 22 patients with second primary malignant tumor (SPMT) which developed in the area of treatment of IPMTs. Group II: 4 patients with SPMT following intracavitary or interstitial radium therapy to IPMTs in other areas. Group III: 12 patients with SPMT following external beam irradiation to IPMTs in other areas. Group IV: 29 patients with SPMT without history of therapeutic irradiation to IPMTs. Mean age of 22 patients with radiation-induced cancer (Group I) was 61.7 years and latent period was distributed between 7 and 33 years, with the mean of 14.7 years. IPMTs of radiation-induced cancer were head and neck cancer or cervical cancer which were usually treated by radiation. There was no close correlation between radiation source and latent period, nor between radiation dose and latent period, but the latent period tended to be longer in patients with SPMTs following radium therapy to IPMTs. Many patients with radiation-induced cancer were improved by radiation therapy and crude 3-year survival rate was 31.6%. Emphasis is made on the fact that radiation therapy is useful for the treatment of radiation-induced cancer. (author)