1993 Volume 5 Issue 3 Pages 209-215
To study the relative risk of second cancer after radiotherapy, we reviewed 2465 cases of uterine cervical cancer who were treated in our institute from 1962 to 1986 and were followed up for more than 5 years. Among them, 1502 cases were treated by radiotherapy with or without surgery (radiotherapy group), and the remainder were treated by surgery only (surgery only group). We defined second cancer as malignancy that occurred in another organ after an interval of 5 years or more from the end of treatment of the first cancer. The relative risk of second cancer was computed by the person-year method advocated by Schoenberg. Second cancer was observed among 8 cases of the surgery group, whereas 43 cases were observed among the radiotherapy group. The cases were: rectal cancer, 6 cases; bladder cancer, 4 cases. The observed and expected ratio (O/E ratio) was 4.02 in rectal cancer and 7.98 in bladder cancer. This incidence of the both cancers was significantly high in the radiotherapy group. Three of the 6 cases with rectal cancer underwent operation in our institute. The incubation periods between the first and second cancers were from 9 to 21 years. Each case exhibited symptoms of chronic radiation proctitis after radiotherapy for uterine cervical cancer. It is thought necessary to follow up such cases carefully to detect radiation induced cancer.
