Irinotecan and radiosensitization in rectal cancer

Neoadjuvant radiation therapy with concurrent 5-fluorouracil-based chemotherapy is currently considered the standard of care for locally advanced rectal cancer. Pathologically complete response is a desirable outcome and has been associated with increased disease-free survival. There is a need to improve on this approach given that only approximately 10% achieve a pathologically complete response. Irinotecan has an established role in the treatment of metastatic rectal cancer. Both in-vitro and in-vivo data have shown promising radiosensitization properties. This study provides an overview of the published clinical trials evaluating the role of irinotecan as a radiosensitizer in the management of locally advanced rectal cancer. Although early-phase clinical trials initially showed promising results, this did not translate into improved outcome in a larger randomized phase II trial. Increased topoisomerase I expression has recently been identified as a possible predictive marker for improved response to irinotecan-based radiosensitization. This finding could help identify a subset of patients more likely to benefit from the addition of irinotecan in future trials.