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PROMISING NEW DRUGS AND COMBINATIONS |
a Memorial Sloan-Kettering Hospital, New York, New York, USA; b Centre Rene Gauducheau, Nantes, France; c Pharmacia Corporation, Peapack, New Jersey, USA; d Aventis, SA, Antony, France
Correspondence: Leonard B. Saltz, M.D., Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021, USA. Telephone: 212-639-2501; Fax: 212-794-7186; e-mail: saltzl{at}mskcc.org
| ABSTRACT |
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Methods. Patients were randomly assigned to receive 5-FU/LV, either alone, or with concurrent irinotecan. The study conducted primarily in North America (study 1), employed bolus 5-FU/LV schedules, while the study performed primarily in Europe (study 2), employed infusional 5-FU/LV regimens. Major endpoints included tumor response rate, time to tumor progression (TTP), overall survival, quality of life, and safety.
Results. In study 1, the respective confirmed response rates for irinotecan/5-FU/LV versus 5-FU/LV were 39% and 21% (p < .001); median TTPs were 7.0 months and 4.3 months, respectively (p = .004). In study 2, response rates for irinotecan/5-FU/LV versus 5-FU/LV alone were 35% and 22% (p = .005); median TTPs were 6.7 months and 4.4 months, respectively (p < .001). Survival time increased significantly with irinotecan/5-FU/LV versus 5-FU/LV alone in both studies (study 1: median 14.8 months versus 12.6 months, p = .042; study 2: median 17.4 months versus 14.1 months, p = .032). The combined analysis of the data from the two studies showed median survivals of 15.9 months versus 13.3 months, favoring the irinotecan-containing combinations (stratified-by-study p = .003). Patients in study 1 had a 36% lower risk of tumor progression and a 20% lower risk of death with the irinotecan combination than with 5-FU/LV alone; comparable risk reduction values in study 2 were 42% and 23%. While grade 3 diarrhea and vomiting were more common with irinotecan/5-FU/LV, grade 4 neutropenia, neutropenic fever, and mucositis were less common with irinotecan/5-FU/LV than with the Mayo Clinic 5-FU/LV regimen.
Conclusion. The combination of irinotecan/5-FU/LV is superior to 5-FU/LV alone as first-line therapy for patients with metastatic colorectal cancer, offering consistently improved tumor control and prolonged survival. Irinotecan-based combination therapy sets a new survival standard for the treatment of this life-threatening disease.
Key Words. Irinotecan • Fluorouracil • Leucovorin • Camptothecin • Antineoplastic agents • Colorectal neoplasms • Quality of life • Randomized controlled trials • Human • Prognosis
| INTRODUCTION |
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Irinotecan (CPT-11, CAMPTOSAR®, Pharmacia Corporation; Peapack, NJ; CAMPTO®, Aventis SA, Antony, France), a topoisomerase I inhibitor, offers a mechanism of action completely different from that of 5-FU in the treatment of colorectal cancer. Irinotecan and its metabolites bind to a complex of DNA and topoisomerase I (an enzyme required for unwinding of DNA during replication), inducing DNA strand breaks and consequent tumor cell death [4]. Irinotecan has shown antitumor activity in patients with colorectal cancer when administered alone as first-line therapy [5-8] or as second-line therapy after 5-FU failure [5, 7-9]. In two randomized phase III studies in patients who experienced failure of first-line 5-FU, irinotecan was compared with either best supportive care or with intensive 5-FU-based infusional therapy. Both studies showed a statistically significant survival benefit for patients treated with irinotecan [10, 11]. The activity of irinotecan against untreated and 5-FU-resistant colorectal cancer led to studies of this agent in combination with 5-FU/LV as first-line therapy for this disease.
Recently Douillard et al. and Saltz et al. reported the results of two studies conducted in parallel at a combined total of 154 institutions located primarily in North America and Europe [12, 13]. These studies evaluated irinotecan combined with either bolus (study 1: Saltz) or infusional 5-FU/LV (study 2: Douillard) in previously untreated patients with metastatic colorectal cancer. Both studies demonstrated statistically significant clinical benefits with the irinotecan/5-FU/LV combinations, including improved tumor control and prolonged survival. The major efficacy and safety results of these studies are summarized in this review.
| PATIENTS AND METHODS |
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In study 1, patients were prospectively stratified according to age (<65 or
65 years), time from initial diagnosis (<6 or
6 months), performance status (0 or 1-2), and prior adjuvant 5-FU-based therapy (yes or no). The patients were then randomized to one of three treatment regimens: irinotecan/bolus 5-FU/LV, bolus 5-FU/LV, or irinotecan alone. The treatment scheme for study 1 is depicted in Figure 1
. In study 2, each study site chose one of two infusional regimens for administration of 5-FU/LV according to local clinical practice or preference, i.e., either the once-weekly regimen of the Arbeitsgemeinschaft Internische Onkologie (AIO) cooperative German group for oncology [14] (designated A1 and B1 in Fig. 1
), or the every-two-week regimen of de Gramont [15] (designated as A2 and B2 in Fig. 1
). Once a site selected its preferred regimen (either AIO or de Gramont), patients at the site were randomized to receive that method of 5-FU/LV administration, with or without irinotecan. After initial treatment, doses in all treatment arms of both studies could be adjusted according to specified guidelines to accommodate individual patient tolerance to the study drugs [12, 13]. Treatment was continued until tumor progression, the occurrence of unacceptable toxicity, or the patient withdrew consent.
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| EVALUATIONS |
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Safety was evaluated in terms of adverse events, laboratory abnormalities, and deaths. Adverse-event assessments and complete blood counts were performed weekly, and chemistry studies were performed at the beginning of each chemotherapy cycle.
| STATISTICAL METHODS |
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For both studies, time-to-event endpoints (e.g., duration of response, TTP, survival) were analyzed by Kaplan-Meier curves and unstratified log-rank tests. Response rates were compared using chi-square tests. The influence of stratification factors and other baseline characteristics on confirmed objective tumor response rates were assessed using multiple logistic regression modeling. Similarly, TTP and survival were assessed using Cox proportional hazard regression modeling. Changes in QOL subscale scores were assessed using analysis of variance for repeated measures. In study 1, worst changes from baseline were compared with Student's t-tests.
Irinotecan alone was included as a third treatment arm in study 1 only to document the efficacy and safety associated with its first-line single-agent use; consequently no hypotheses regarding its comparative efficacy were tested.
| RESULTS |
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With respect to baseline laboratory values, carcinoembryonic antigen (CEA) and total bilirubin levels were generally similar across the two studies. However, there were notably greater proportions of patients with a depressed hemoglobin level, elevated WBC, or abnormal serum lactate dehydrogenase (LDH) in study 1 than in study 2. These laboratory abnormalities are consistent with the performance status findings, possibly indicating greater tumor burden or tumor-related organ dysfunction among the patients in study 1.
| EFFICACY |
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| RESPONSE RATES |
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50% on at least one occasion) was significantly higher for patients treated with irinotecan/5-FU/LV than for those treated with 5-FU/LV (50% versus 28%, p < .0001); comparable rates were also significantly higher in study 2 (49% versus 31%, p < .001). The confirmed response rates (based on responses confirmed by imaging tests
4 weeks later) were also significantly (p < .005 to p < .001) and consistently higher among patients who received irinotecan/5-FU/LV compared with those who received 5-FU/LV in both studies (Table 3
CEA
Serum CEA was assessed systematically during study 1. CEA response (
50% decrease from baseline in serum CEA during treatment) was evaluated in patients with elevated baseline CEA values and at least one CEA assessment while on treatment. The CEA response rate with irinotecan/ 5-FU/LV was substantially higher than with 5-FU/LV; this difference was significant (p < .001) (Table 3
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TTP
TTP was significantly longer in both studies for patients who received irinotecan/5-FU/LV than for those who received 5-FU/LV (study 1: median 7.0 months versus 4.3 months, p = .004; study 2: median 6.7 months versus 4.4 months, p < .001). As in the case of response rate, TTP was universally improved in all patient subgroups [16]. Kaplan-Meier TTP curves for both studies are shown in Figure 2
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Single-Agent Irinotecan Results
A single-agent irinotecan arm was included in study 1 only to document the activity of this agent as monotherapy. Efficacy results in this arm of the study appeared generally similar to those observed with 5-FU/LV alone (Table 3
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Post-Study Treatment
Over 90% of the patients had follow-up information regarding post-study anticancer therapy. In study 1, 52% of these patients in the irinotecan/5-FU/LV-treated arm received some form of second-line therapy, compared with 70% in the 5-FU/LV-treated arm. For 56% of the patients in the 5-FU/LV arm, this second-line regimen consisted of irinotecan as a single agent or in combination. In study 2, 49% of patients in the irinotecan/5-FU/LV arm received post-study therapy compared with 65% of those in the 5-FU/LV arm. In this study, 34% of the 5-FU/LV-treated patients given post-study chemotherapy received second-line irinotecan (Table 4
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| SAFETY |
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For neutropenia, only grade 4 events are usually associated with clinical consequences. Of interest, the frequency of grade 4 neutropenia with combination irinotecan/5-FU/LV therapy (24%) in study 1 was essentially half that observed in patients receiving 5-FU/LV in the control group (43%) and proportionately fewer patients experienced neutropenic fever when contrasting irinotecan/5-FU/LV (7%) with 5-FU/LV (15%). In study 2, where schedules of chemotherapy administration were similar, grade 4 neutropenia was more frequently seen when irinotecan was added to 5-FU/LV (10%) than with 5-FU/LV alone (1%). The incidence of neutropenic fever was also higher in the irinotecan/5-FU/LV arm (5.0%) than in the 5-FU/LV arm (1%); however, these rates of neutropenic complications are quite low when contrasted with many other chemotherapy regimens [21].
Discontinuations due to adverse events were acceptably low across all arms of both studies. The incidence of treatment-related death ranged from 0% to 1% in all treatment groups.
| QOL |
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| DISCUSSION |
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The two phase III randomized multicenter, multinational, controlled studies reviewed here compared the efficacy and safety of new combinations of irinotecan/5-FU/LV to that of traditional regimens of 5-FU/LV given as first-line therapy of metastatic colorectal cancer. The studies were similar in that they enrolled analogous patient populations, evaluated similar efficacy and safety endpoints, and applied standardized methods of analysis. The trials were complementary in that they assessed the use of irinotecan in combination with two different methods of 5-FU/LV administration (bolus and infusional therapy). Study 1 compared a new combination of irinotecan/bolus 5-FU/LV with that of the Mayo Clinic regimen of bolus 5-FU/LV that had been most widely employed in North America. Study 2 symmetrically determined the therapeutic ratio associated with adding irinotecan to two different infusional 5-FU/LV regimens that were widely used in Europe. Because the comparator regimens have been commonly used in oncology practices worldwide, the two studies provide clinicians with insights into the efficacy and safety of the new combinations relative to familiar standards.
The efficacy results of the two studies were remarkably consistent and show that the combination of irinotecan with 5-FU provides patients with significant reductions in tumor size in conjunction with prolonged suppression of tumor growth. The confirmed objective response rates with the irinotecan/5-FU/LV arms (39% and 35%) were 1.5 to 2 times those in the 5-FU/LV arms (21% and 22%), and these differences were statistically significant. In studies 1 and 2, respectively, TTP was significantly improved with combination treatment (medians, 7.0 and 6.7 months) relative to treatment with 5-FU/LV alone (medians, 4.3 and 4.4 months). Assessment of response rates and TTP across demographic and disease-related subgroups showed improvements with irinotecan-based combination therapy in all prospectively defined subgroups [16]. These results indicate that irinotecan/5-FU/LV has the potential to offer better tumor control to all patients who are eligible for first-line combination chemotherapy.
The most important finding of the studies was that first-line irinotecan/5-FU/LV combination treatment provided a statistically significant survival advantage. It is particularly noteworthy that this advantage occurred even though most control patients received second-line irinotecan therapy after on-study failure of 5-FU/LV. These results suggest that early combination irinotecan/5-FU/LV may be superior to sequential administration of first-line 5-FU followed by second-line irinotecan. The combination therapy survival outcomes noted among patients with good performance status accentuate this observation [16]. Such findings were presaged by the results of a prior study in metastatic colorectal cancer in which early administration of chemotherapy before symptom development was compared with delayed treatment after symptom development; as in the current experience, early therapy in that study resulted in significantly better survival [23].
Cox regression modeling, which assessed treatment effect adjusted for significant prognostic factors, provided further evidence that combination therapy with irinotecan/5-FU improves TTP and survival. This analysis indicated that irinotecan/5-FU/LV treatment resulted in an approximate 40% reduction in the relative risk of tumor progression and a 20% decrease in the relative risk of death.
In both studies, gastrointestinal toxicities were more common with combination treatment, but grade 4 diarrhea largely defined by the need for hospitalization for supportive carewas infrequent (<8%). In study 1, grade 4 neutropenia, neutropenic fever, and mucositis were observed less often with weekly irinotecan/5-FU/LV than with Mayo Clinic bolus 5-FU/LV alone; data from other studies that compared weekly versus monthly 5-FU/LV therapy [24, 25] suggest that this reduced toxicity with combination therapy is most likely due to the differences in 5-FU/LV scheduling between the arms. In study 2, clinically relevant grade 3 and 4 events, e.g., vomiting, mucositis, and neutropenic fever, were infrequent with the de Gramont irinotecan/5-FU/LV regimen. The safety findings were supported by the results of the QOL analyses, which showed that administration of irinotecan in combination with 5-FU/LV did not result in significant worsening of QOL.
Attempts to improve outcomes in patients with metastatic colorectal cancer with the limited tools of 5-FU and LV have been the source of decades of frustration and disappointment. Irinotecan has now broken the barrier to improved survival, first as single-agent second-line therapy, and now as a component of first-line combination treatment. The studies discussed here are the first trials to document that the combination of a new agent with 5-FU/LV can safely benefit patients with metastatic colorectal cancer by inducing tumor shrinkage, extending tumor control, and significantly prolonging life without an impairment of QOL. The strength and consistency of the data from these large complementary studies led the FDA's Oncology Drug Advisory Committee (ODAC) to conclude that irinotecan/5-FU/LV should be the reference standard against which future first-line therapies for metastatic colorectal cancer are compared.
Given the positive findings in patients with metastatic disease, several trials in the U.S. and Europe are comparing irinotecan/5-FU/LV with 5-FU/LV as adjuvant therapy for patients with stage III colon cancer; it is hoped that the addition of irinotecan to 5-FU/LV will offer an increased opportunity for cure in patients with early-stage disease.
| Related articles in The Oncologist: Irinotecan: A New Agent Comes of Age. Saltz LB. The Oncologist 2001;6:65. Irinotecan (CPT-11): Recent Developments and Future DirectionsColorectal Cancer and Beyond. Rothenberg ML. The Oncologist 2001;6:66-80.
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| ACKNOWLEDGMENTS |
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L.S. and J-Y.D. have received major research support and honoraria as consultants for both Pharmacia Corporation and Aventis Corporation.
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