Toxicity associated with adjuvant postoperative therapy for adenocarcinoma of the rectum.
The Gastrointestinal Tumor Study Group's (GITSG) adjuvant rectal carcinoma study compared four postoperative treatment regimens: (1) control (no adjuvant therapy); (2) chemotherapy alone consisting of pulses of 5-fluorouracil and methyl CCNU for 18 months; (3) pelvic and perineal radiotherapy using parallel opposed fields with 4000 rad in 4.5 to 5 weeks or 4800 rad in 5 to 5.5 weeks; and (4) a combination of both modalities. The results of this study are published elsewhere and show a significantly reduced recurrence rate and prolonged disease-free survival time for the combined modality arm compared with the no therapy arm. Severe toxicity in the combined therapy arm was significantly worse (P less than 0.001) than in either single modality arm. Most of the differences in toxicity experienced between the three regimens involved diarrhea, thrombocytopenia, and leukopenia. Analysis of all parameters of radiotherapy quality assurance data was not significantly associated with toxicity. Radiation enteritis was noted in 5 patients of 96 (5.2%) in the two arms containing irradiation. All five required laparotomy. The two enteritis fatalities occurred late at 605 and 1000 days after start of combined modality treatment, respectively. One other patient on the chemotherapy arm died of acute nonlymphocytic leukemia. The authors conclude that combined radiotherapy and chemotherapy, although significantly more effective in reducing recurrence than no therapy, is significantly more toxic than single-modality therapy in many parameters, although most of the toxicity is transient and therefore not limiting. Late complications, which are less reversible and therefore much more important than early reactions, and radiation enteritis in this study were relatively uncommon. This schedule of combined modality therapy is not only effective but appears to have tolerable toxicity, because of the relative lack of late effects.