Irinotecan in the treatment of colorectal cancer

Irinotecan, a water-soluble, semisynthetic derivative of camptothecin, is a key component of first- and second-line treatment regimens for metastatic colorectal cancer (CRC). In the first-line treatment of metastatic CRC, the results of two prospective, multicenter phase III trials have shown that the combination of irinotecan with bolus or infusional 5-fluorouracil (5FU)/leucovorin (LV) can significantly prolong survival compared with 5FU/LV alone, with a manageable side effects profile. In addition, irinotecan-based regimens, with or without oxaliplatin, may improve resectability of metastases and further increase patient survival. Studies of irinotecan in the first-line setting in combination with newer agents, such as bevacizumab, have shown impressive overall survival. In the second-line setting, irinotecan has demonstrated efficacy superior to that of best supportive care. Initial studies of irinotecan plus bolus 5FU/LV, and the preliminary results from trials of irinotecan plus infusional 5FU/LV in the adjuvant setting, have been disappointing; however, for the largest trial, the Pan-European Trial in Adjuvant Colon Cancer, results with sufficient follow-up are pending. Irinotecan has an acceptable tolerability profile and is not associated with cumulative toxicities in patients with metastatic CRC; regimens containing irinotecan extend treatment duration and improve survival. New regimens and adjunctive therapies are being explored to reduce the incidence of common complications of irinotecan treatment, such as diarrhea and neutropenia.

Advances in the treatment of metastatic colorectal cancer

The overall 5-year survival rate for patients with metastatic colorectal cancer (CRC) is less than 10%. Median survival with 5-fluorouracil (5-FU)/leucovorin (LV) therapy is approximately 12 months. Recent additions to the chemotherapy armamentarium for this disease have begun to prolong median survival times. In trials in which patients are exposed to all three approved chemotherapy agents, oxaliplatin, irinotecan, and 5-FU/LV, or capecitabine during the course of their disease, median survival has reached 20 months. The addition of oxaliplatin and irinotecan to 5-FU/LV regimens has also led to the maintenance of quality of life for longer intervals than were traditionally observed with 5-FU/LV alone. Current standard first-line regimens for metastatic CRC are FOLFOX (infusional 5-FU/LV with oxaliplatin) and FOLFIRI (infusional 5-FU/LV with irinotecan). The addition of bevacizumab to a two-drug regimen (irinotecan with 5-FU/LV) prolongs median survival to 20 months, with a modest amount of additional toxicity. Improvements in this median survival have not yet been realized with modifications to the current standard regimens; however, the oral agent capecitabine appears to be a reasonable substitute for infusional 5-FU/LV in combination regimens or as a single agent, with the advantage of reducing the inconvenience of the long infusion time. Ongoing investigations will identify a place for capecitabine, epidermal growth factor inhibitors, and new cytotoxics in the treatment of metastatic CRC.