Preoperative radiation therapy for locally advanced carcinoma of the rectum. Clinicopathologic correlative review.

During a three-year period, 27 patients with the diagnosis of adenocarcinoma of the rectum were referred to the Department of Radiation Oncology and accepted for preoperative radiation therapy. The referral was based solely on endoluminal ultrasound staging (ELUS) of an unfavorable lesion (n = 12) or ultrasound staging with the clinical impression of a fixed (n = 9) or tethered (n = 6) lesion. High-dose (4,500-5,600 cGy) preoperative radiation was followed by definitive surgery in four to seven weeks. The gross and microscopic pathology observed in 23 specimens of this group of patients formed the basis of this report. The microscopic findings that persist after radiation allow an accurate determination of the tumor stage existing prior to radiation. Correlations are made between the original evaluation of the tumor, including ELUS, and the microscopic findings. ELUS accurately predicted the depth of tumor penetration in 20 to 23 of 23 specimens and the lymph node status in 16 of 23 specimens. In the context of the pathologic findings as described, downstaging was not demonstrated. Following this radiation protocol, a marked reduction in tumor mass was demonstrated, as well as evidence of tumor destruction in the remaining mass, varying from minimal to total elimination of viable tumor. The concept that radiation fibrosis exists only as it approximates or replaces neoplasm is offered. In the context of this pathologic finding, improved resectability occurred for certain tumors. It is recommended that ELUS be added to the clinical evaluation of rectal adenocarcinoma. It is also recommended that the pathologic findings described be used when reporting the stage of rectal tumors that have received high-dose preoperative radiation therapy.