Radiation Therapy for Resectable Colon Cancer
Radiation Therapy for Resectable Colon Cancer
The role of adjuvant radiation in the treatment of colon cancer has been controversial since the seminal report from Gunderson and Sosin examining the patterns of failure after reoperation. In subsets of patients with high-risk features such as T4 and/or node-positive disease in fixed sites in the colon, the incidence of a local failure as a component of failure was almost 50%. Based on these data as well as subsequent reports from other institutions,[2,3] Dr. Willett and his group at the Massachusetts General Hospital retrospectively examined the role of locoregional radiation. They reported a local control benefit in selected patients with T3 or T4, node-positive disease. These encouraging findings lead to the development of the phase III INT 0130 trial of fluorouracil (5-FU)/levamisole (Ergamisol)which was standard of care at that timewith or without locoregional radiation. The trial did not confirm a local control or survival advantage when locoregional radiation was added to postoperative chemotherapy.
Should the Trial Be Repeated?
In the comprehensive and thought-provoking review by Czito et al, the authors review the rationale and results of INT 0130, emphasizing its primary shortcomingthe suboptimal accrual that left the trial underpowered to answer the primary objective. In addition, it is unclear how relevant these data are today, given the significant advances in systemic chemotherapy and multiple regimens both available and in development.
Given the incomplete accrual of INT 0130 coupled with advances in systemic chemotherapy, should the trial be repeated? Is it still reasonable to recommend locoregional radiation for selected patients who, based on patterns of failure determined in an era when chemotherapy was not routinely delivered, are at high risk for local recurrence? Furthermore, has more effective chemotherapy changed the incidence of locoregional failure? Lastly, as reported in the INT 0114 trial of postoperative adjuvant therapy for rectal cancer, will such treatment only delay late local recurrences? The short answer to these questions isunknown. The ideal source for patterns-of-failure data is large phase III adjuvant trials such as intergroup trials. Unfortunately, it is difficult to obtain accurate local recurrence data from these trials as most examine first failure rather than cumulative failure. This method underestimates the true incidence of failure because, after the initial failure site is found, subsequent sites (if and when they develop) may not identified. Systemic chemotherapy may alter both the time and patterns of local recurrence. Until such trials capture this information, the ability to accurately assess patterns of failure will be limited.
Conclusions Given the availability of more active chemotherapeutic regimens, the shortcomings of retrospective data, and an underpowered randomized adjuvant trial, what is the role of locoregional adjuvant radiation in patients with colon cancer? Dr. Czito et al offer reasonable recommendations. In general, patients with T4 colon cancer adherent to a fixed pelvic structure are treated as if they have rectal cancer, receiving preoperative combined pelvic irradiation and chemotherapy. For patients with primary tumors in the abdomen, postoperative combined radiation therapy plus chemotherapy is limited to settings where the margins are close or positive. In the future, as molecular marker information obtained from the current phase III adjuvant colon cancer trials is correlated with patterns of failure, more informed decisions will likely be possible.
Bruce D. Minsky, MD
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