Colorectal cancer after pelvic irradiation: case reports.

Four patients with colorectal cancer after pelvic irradiation for gynaecological malignancies are reported. The interval between irradiation and the diagnosis of colorectal cancer was 15-28 years. Histological findings of radiation proctocolitis adjacent to the cancer were observed in all specimens. Ki-67 immunohistologic staining showed high cell proliferation activity in the irradiated mucosa of a recently removed specimen. Although irradiation has not been proved to induce colorectal cancer, considerable circumstantial evidence supports this belief. Awareness of this potential long-term complication is important when planing the follow-up of patients subjected to pelvic radiotherapy.