Colorectal cancer after intrapelvic radiation

From 1946 to 1990, 2909 cases of colorectal cancer were surgically treated. Twenty-nine (1%) of these had history of intrapelvic radiation for malignancy such as uterine cancer. The mean interval from the end of radiotherapy to the resection of colorectal cancer was 17 years and 5 months (range: 2 years 6 months to 35 years). Histologically, of 29 cases and 30 lesions, there were 3 cases (10%) of very well-differentiated adenocarcinoma, 19 (63%) of well to moderately differentiated adenocarcinoma, 7 (24%) of mucinous carcinoma (MUC), and 1 (3%) of squamous cell carcinoma. The 5 year survival rate was 68%. For MUC alone, it was 100% (for MUC without radiotherapy, 33%). The 24% incidence of MUC in this series is higher than that (5%) of a general population. The longer the radiotherapy-to-resection interval, the more frequent the incidence of MUC as well as of radiation proctitis (19 cases). Associated with radiation proctitis were adenoma (5 cases), dysplasia (5 cases) and colitis cystica profunda (7 cases). We hypothesize that MUC in this series stems largely from radiation proctitis. (author)