Irinotecan in metastatic colorectal cancer: Dose intensification and combination with new agents, including biological response modifiers

Phase I/II studies suggest that the combination of irinotecan with capecitabine is feasible and has promising activity. Diarrhea and neutropenia are dose limiting. Overall response rates (RRs) in the 40% to 60% range are seen from preliminary data. Work in progress is assessing the combination of irinotecan with UFT/leucovorin (LV). The use of irinotecan together with raltitrexed is also being investigated, as is its combination with oxaliplatin. Two phase II studies of irinotecan plus oxaliplatin in second-line patients report median survivals of 11-12 months. It seems possible to safely escalate the dose of single-agent irinotecan to 500 mg/m² in patients showing good tolerance of the drug. Irinotecan can be used in combination with LV5FU2 at doses up to 260 mg/m², especially if only one bolus of 5-fluorouracil (5-FU) is given. Control of tumor growth is achieved in 90% of patients. Preliminary data suggest that regimens based on 5-FU/LV and irinotecan can safely be combined with the anti-epidermal growth factor receptor (EGFR) antibody cetuximab. In patients with EGFR-positive tumors, this may prove an effective means of increasing response rate or combating treatment resistance. Following evidence that COX-2 inhibition can slow progression in familial adenomatous polyposis, celecoxib is to be studied in metastatic colorectal cancer (CRC). In vitro, the cyclin-dependent kinase inhibitor flavopiridol enhances the induction of apoptosis by chemotherapy. Clinically, it can safely be administered with irinotecan, and studies in CRC are planned.