Rectal cancer after pelvic irradiation.

During a 6 month period in 1988 five women were treated at Colchester General Hospital for carcinoma of the rectum, each more than 10 years after undergoing pelvic irradiation. Although irradiation has not been proven to induce human colorectal cancer, considerable circumstantial and experimental evidence supports this belief. Features suggestive of radiation-induced colorectal cancer are the presence of radiation-damaged bowel adjacent to the carcinoma and a mucus-secreting ('colloid') histological pattern. The increasing number of women being exposed to rectal irradiation in the course of treatment of gynaecological malignancy may result in an increase in the incidence of radiation-induced rectal cancer. Awareness of this potential long-term complication is important when planning follow-up of patients subjected to pelvic radiotherapy.