In Europe and the United States, the incidence of breast cancer is increasing, and metastatic breast cancer presents a growing therapeutic challenge. While many combination chemotherapy regimens result in high response rates, complete remissions (CRs) occur in less than 20% of patients with metastatic breast cancer and the median survival is generally about 2 years.
After patients fail primary therapy for metastatic disease, CRs are infrequent; overall response rates for most regimens range from 10% to 35%. Given the dearth of active agents capable of inducing durable CRs in metastatic breast cancer, the need for new therapeutic strategies, as well as the incorporation of new drugs into these strategies, is abundantly clear.
Results of clinical studies suggest that fluorouracil (5-FU) administered by continuous infusion has significant clinical activity in heavily pretreated patients with breast cancer, with reported response rates of 25% to 40%.[2-4] A substantial body of experimental data has been developed, indicating that the addition of pharmacologic concentrations of reduced folates to human tumor cells in vitro enhances both the duration and degree of thymidylate synthase inhibition produced by 5-FU.[5-7]
Especially in colorectal carcinoma, folinic acid (FA) has been shown to enhance the therapeutic activity of 5-FU.[8-11] To extend this area of biochemical modulation and build on the results using monthly 5-FU/FA for advanced colorectal carcinoma, several groups performed phase II trials using this combination in the treatment of pretreated patients with metastatic breast cancer.[1,12] The results of these studies suggest that 5-FU/FA has a significant therapeutic effect and can be administered with an acceptable level of toxicity as palliative treatment. Furthermore, phase II studies with FA/5-FU in colorectal cancer suggest that weekly administration of high-dose FA in combination with high-dose 5-FU (given as a 24-hour continuous intravenous infusion) induces higher overall response rates. How do these data affect our clinical efforts in breast cancer? Results of several phase II trials indicate that 5-FU/FA is active in anthracycline-pretreated patients with breast cancer.[1,14-16] In these trials, FA and 5-FU were usually administered by bolus injection. However, our experimental and clinical data indicate higher activity when the combination is given as a protracted IV infusion.[2-4]
Based on those results, we undertook a phase I/II study with weekly high-dose 5-FU/FA in heavily pretreated breast cancer patients. Our data demonstrated that FA and 5-FU can be safely administered at high dosesFA 500 mg/m2 via 2-hour IV, followed by 5-FU 2 g/m2 IV over 24 hours given once weekly for 6 weeks with 2 weeks rest. The response rate in the 32 phase II patients was 41% (95% confidence interval, 24% to 58%), with a median response duration of 11 months. Study patients had at least two prior treatment regimens for metastatic breast cancer. The results persisted among anthracycline-resistant patients. Our encouraging data using weekly high-dose 5-FU/FA against heavily pretreated breast cancer patients and the promising antineoplastic activity of the tubulin-binding agent paclitaxel (Taxol, Bristol- Myers Squibb Company) given as second-line, single-agent chemotherapy in metastatic breast cancer [18-24] led to the initiation of our phase I/II study of paclitaxel in combination with weekly high-dose 5-FU/FA.
Patients were treated with weekly high-dose 5-FU (via 24-hour infusion)/FA (2-hour infusion prior to 5-FU) for 6 weeks; paclitaxel (3-hour infusion) was administered on days 1 and 22 after standard premedication. Each treatment cycle comprised 6 weeks, followed by 2 weeks rest. All patients were treated under outpatient conditions using IV port systems and portable pumps. A classic phase I trial preceded the phase II study.
In all, 16 patients entered phase Ifour patients at each dose level. The 16 patients received 56 treatment cycles. No dose-limiting toxicities occurred at dose levels 1 to 3. Because of moderate toxicity observed at dose level 4, together with partial responses seen at all dose levels, we chose dose level 4 for evaluation during phase II (Figure 1). To date, 46 patients have been enrolled in phase II.
Of the 46 enrolled patients, 35 are evaluable for response; data from 11 patients are too early to evaluate. Eligible patients had the characteristics and patterns of pretreatment shown in Table 1 and Table 2. Among 46 patients and in 108 treatment cycles (median, three treatment cycles per patient; range, one to five), World Health Organization grade 3 alopecia was frequent. Other toxicities occurred as shown in Table 3. No serious acute paclitaxel hypersensitivity reactions were observed. Neutropenia was common but generally mild to moderate. No hospitalizations were necessary for febrile neutropenia. The duration of grade 3/4 neutropenia was generally brief, and no cytokines were used. Nonhematologic toxicities consisted mainly of mild to moderate myalgia, diarrhea, mucositis, nausea/vomiting, and hand-foot syndrome (Table 3). Peripheral neuropathy was cumulative; it appeared primarily during the third treatment cycle and was mild to moderate in severity.
More than half of the patients responded to the study regimen, including one CR (3%) and 18 partial remissions (51%). Disease was stable in 40% of patients (14/35) and progressed in 6% (2/35). Overall response rate was 54% (95% confidence interval, 37% to 69%) (Table 4). Among the 20 patients with anthracycline-resistant disease (defined as progression while receiving previous anthracycline-containing chemotherapy), 55% responded to the study regimen (11/20; 95% confidence interval, 34% to 76%) (Table 5). Time to maximum response is 2 months (range, 1 to 5), remission duration is 8+ months (range, 2 to 11), and median follow-up is 6 months.
These results should be considered in the context of phase II studies in metastatic breast cancer, and anthracycline-resistant disease in general. Anthracycline-resistant breast cancer is a negative prognostic factor for response to salvage chemotherapy. The collected phase II experience shows that second- or third-line chemotherapy after prior exposure to anthracyclines induces 15% to 30% objective remissions at best. With conventional doses of 5-FU/FA, a 29% response rate was achieved in patients with one prior treatment regimen, and a cumulative response rate of 22% in patients with two prior treatment regimens, respectively.[1,12,14-16] With a weekly high-dose, 24-hour schedule of combination 5-FU/FA, the achieved results seem to be superior to those of conventional 5-FU/FA bolus therapy, as discussed previously. With the introduction of a new class of active drugs in breast cancer, the taxanes, paclitaxel offered an additional chance to improve therapeutic outcome.[18-23]
In this, as well as in other phase I/II studies, we could demonstrate that other drugs (eg, cisplatin [Platinol], paclitaxel) can safely be added to weekly high-dose infusional 5-FU, without compromises in dose and dose intensity, and without intolerable toxicity. The latter fact is crucial to the palliative treatment intention associated with salvage chemotherapy patients with advanced breast cancer. Furthermore, the combination of paclitaxel with weekly high-dose 5-FU/FA is well tolerated and can be safely administered under outpatient conditions. Despite the use of full doses of both drugs, only 14% and 7% of all treatment cycles were associated with World Health Organization grade 3/4 myelotoxicity and diarrhea, respectively. Most side effects were mild and of short duration. Of note is the 54% response rate induced by high-dose 5-FU/FA/paclitaxel in patients with prior chemotherapy, and especially in patients with anthracycline-resistant disease (response rate, 55%). These results are noteworthy, especially when compared with results reported with other combinations in the second-line treatment of advanced breast cancer.
UFT1-(2-tetrahydrofuryl)-5-fluorouracil (tegafur) and uracil in a molar ratio of 1:4is an orally available agent that appears to have activity comparable to intravenously administered 5-FU in combination with leucovorin. In our new study, we therefore plan to substitute oral UFT plus leucovorin for high-dose 5-FU/FA. Oral UFT given daily for 14 days allows prolonged exposure to the drug without the need for a central catheter or an infusion pump. Considering the clinical and experimental data, the combination of paclitaxel with UFT and leucovorin warrants investigation as salvage chemotherapy in patients with metastatic breast cancer. The appropriate dose schedule for this combination will be determined in a phase I study, which began in May 1997.
Fluorouracil is the classic example of a cycle-specific, S-phase-dependent drug with a short half-life of 10 to 20 minutes. It is therefore reasonable to postulate that conventional bolus injection may well not be the most effective schedule. With the introduction of oral UFT, and, therefore, the bioavailability of oral 5-FU, the story is unfolded again.
Such agents, already used in clinical trials, may allow the administration of long-term, low-dose oral 5-FU with the same pharmacokinetic profile achieved by continuous IV infusion. Finally, it would also be of interest to see a randomized comparison of oral UFT and/or continuous-infusion 5-FU in combination with paclitaxel as first-line chemotherapy for the palliation of advanced breast cancer evaluated against conventional schedules, with toxicity and quality-of-life measures in addition to the usual efficacy end points.
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