Chemotherapy of metastatic colorectal cancer

Abstract

Without treatment, patients with inoperable or metastatic colorectal cancer have a median life expectancy of about 8 months. The following article is an update of our 2005 review of chemotherapy regimens used in metastatic colorectal cancer, based on the standard Prescrire methodology. In 2005, the de Gramont protocol, based on fluorouracil (always combined with folinic acid) plus either oxaliplatin (Folfox protocol) or irinotecan (Folfiri protocol), was the standard first-line chemotherapy in this setting. Four trials comparing monotherapy versus combination therapy in previously untreated patients showed that initial fluorouracil (or fluorouracil precursor) monotherapy, followed by the Folfox or Folfiri protocol in case of failure, was not associated with shorter overall survival. Two trials compared first-line treatment with the Folfiri regimen versus the Folfoxiri regimen (fluorouracil + oxaliplatin + irinotecan). One of these studies showed an increase in median survival with the Folfoxiri protocol (24 versus 17 months), but at a cost of greater neurotoxicity. The only tangible advantage of capecitabine and tegafur, two oral fluorouracil precursors, is their convenience of use. Pemetrexed was less effective and more toxic than the Folfiri protocol in one trial. Bevacizumab and panitumumab have yielded disappointing results in previously untreated patients. Neither of these monoclonal antibodies has yet been shown to improve overall survival. Three trials have assessed the addition of cetuximab to combinations consisting of fluorouracil or capecitabine plus oxaliplatin or irinotecan. In two of these trials, the median survival time of patients whose tumours carried the wild-type KRAS gene was about 3 months longer in the cetuximab arms, although the increase was statistically significant in only one trial. Cetuximab had no impact on survival time in the third trial. In two trials, an anti-EGFR antibody (panitumumab or cetuximab) reduced median survival when added to bevacizumab in previously untreated patients. When progression occurs after treatment with the Folfiri protocol (or equivalent), a combination of the Folfox protocol and bevacizumab seems to increase median survival time by about 2 months versus Folfox alone, but it is also more toxic. In patients who progress after receiving the fluorouracil + oxaliplatin combination (Folfox) or the fluorouracil+ irinotecan combination (Folfiri), neither panitumumab nor cetuximab has been shown to provide a clinically meaningful increase in overall survival. It remains to be shown whether these drugs are more effective in patients with the wild-type KRAS gene than in patients with KRAS mutations. In early 2010, the standard cytotoxic drugs for treatment of metastatic colorectal cancer are fluorouracil (combined with folinic acid), oxaliplatin and irinotecan. Initial combination therapy may be beneficial when the metastases are borderline operable. When the metastases are inoperable and are unlikely to become operable after chemotherapy, it seems best to begin treatment with single-agent fluorouracil (+ folinic acid) or capecitabine. The use of monoclonal antibodies in first-line treatment of patients with colorectal cancer is not justified. Further trials of these drugs are warranted as second-line treatment for patients with KRAS wild-type tumours.