Dose-finding and Pharmacologic Study of Chronic Oral Idarubicin Therapy in Metastatic Breast Cancer Patients¹

IDA³ is a DAU analogue that has achieved a clinical role in the treatment of some hematological malignancies (1, 2, 3, 4, 5, 6, 7). Recently, IDA has been also proposed in the management of adult solid tumors (8, 9, 10, 11, 12, 13). IDA is endowed with greater biological activity and lower cardiotoxicity than DAU (2). Our and other in vitro studies have indicated that IDA is more effective than DAU in tumor cell lines displaying the multidrug-resistant phenotype, thus suggesting that IDA could be useful in circumventing multidrug resistance (3, 14).

IDA therapy generally is well tolerated. The main IDA adverse effect is myelosuppression. Gastrointestinal toxicity is also common. This includes nausea, vomiting, and stomatitis of different WHO grades,according to the IDA dose schedule used. G1-G2 diarrhea occurs in ∼10% of patients after a single i.v. dose (10–15 mg/m²) and in 10–30% of patients after oral administration (40–45 mg/m²; Ref. 9).

The pharmacokinetics of IDA have been evaluated in cancer patients after i.v. or oral administration (10, 15). IDA has a large volume of distribution, which probably indicates extensive tissue accumulation. IDA is metabolized, mainly in the liver after oral administration, to IDOL (10). IDOL retains good cytotoxic activity in vitro (15). Variability in oral absorption has been reported both between patients and within the same patient (10).

IDA is the first anthracycline that can be given both p.o. and i.v. Oral IDA has been used in advanced breast cancer (11, 16). However, the role of oral IDA in this tumor needs to be better clarified. The oral route is useful in palliative treatment of patients with poor venous access and may be particularly appropriate for older patients (17). Oral IDA in solid tumors was administered over 1, 3, or 5 days (9). However, as demonstrated previously for other antineoplastic drugs (18, 19), the effectiveness of IDA might improve by low-dose continuous exposure. Although IDA is not a typical cell cycle phase-specific drug, it exerts some antitopoisomerase II activity (1). It has been demonstrated that the commitment to cell killing by antitopoisomerase II agents predominantly occurs in S-phase cells (20). Therefore, prolonged treatments with this drug increase the number of cells exposed to the drug during the most chemosensitive phase of the cell cycle. The increased ratio of IDOL/IDA AUC after oral compared with i.v. administration represents another advantage of prolonged low-dose treatments because IDA and its metabolite can cooperate in determining cytotoxic effects. Finally, the long plasmatic t_1/2 of IDA and the longer t_1/2 of IDOL (10) are pharmacological characteristics extremely favorable in protracted oral drug administration. In fact, they reduce the fluctuations in the plasmatic concentrations of the drug, allowing cells to be exposed to steadier drug concentrations, as with continuous i.v. infusion therapy.

To investigate a simple modality of IDA administration instead of the cumbersome and costly continuous i.v. infusion, a dose escalation of oral IDA was devised. The drug was given p.o. in hyperfractionated doses over a long period of time with the purpose of determining the MTD, toxicity profile, and pharmacokinetics of IDA this schedule.

Thirty-one patients, ages 39–73 years, with histologically confirmed, measurable, and evaluable metastatic breast cancer were eligible for the study. All patients had been pretreated with chemotherapy, including anthracyclines. Pretreatment was adjuvant in seven patients: fluorouracil (600 mg/m²),epirubicin (75 mg/m²), and cyclophosphamide (600 mg/m²; FEC) in three patients; FEC and cyclophosphamide (600 mg/m²), methotrexate (40 mg/m²), and 5-fluorouracil (600 mg/m²) in two patients; and epirubicin (75 mg/m²) and cyclophosphamide (500 mg/m²) in two patients. Median time to recurrence from the end of chemotherapy in these patients was 8 months (range,1–35 months). Chemotherapy for advanced breast cancer had been performed in 24 patients: FEC in 13 patients; fluorouracil (500 mg/m²), doxorubicin (60 mg/m²) and cyclophosphamide (500 mg/m²) in 1 patient; epirubicin and cyclophosphamide in 6 patients; doxorubicin (50 mg/m²) and cyclophosphamide (500 mg/m²) in 1 patient; doxorubicin (50 mg/m²) and cyclophosphamide (500 mg/m²) and Taxotere (100 mg/m²) in 1 patient; and cyclophosphamide-methotrexate-5-fluorouracil in 2 patients. All of the patients had relapsed after adjuvant treatment or had disease progression during chemotherapy. Overall, 28 patients were pretreated with anthracyclines. The median doses of epirubicin and doxorubicin received in previous treatments were 440 mg/m²(range, 155–765 mg/m²) and 180 mg/m² (range, 140–317 mg/m²), respectively.

The patients should not have received chemotherapy and/or radiation within 4 weeks before IDA treatment and were not receiving concurrent hormonal therapy. Patients with a history of cardiac disease were excluded. Other inclusion/exclusion criteria were: normal baseline(≥50%) LVEF; life expectancy of at least 8 weeks; Eastern Cooperative Oncology Group performance status of 0, 1, or 2; WBC count≥4,000/μl; platelet count ≥150,000/μl; ANC ≥2,000/μl;bilirubin level ≤1.5 mg/dl; aspartate aminotransferase level two times normal or lower, serum creatinine level ≤1.5 mg/dl, and creatinine clearance ≥60 ml/min. Written informed consent was obtained before study entry and the protocol was approved by the local Ethical Committee.

Pretreatment evaluation included history and physical examination,chest X-ray, liver ultrasound, electrocardiogram, determination of resting baseline LVEF by echocardiography and computed tomography,total body Tc^m bone scan when clinically indicated, full blood cell count, electrolytes, blood urea nitrogen,creatinine clearance (24-h urinary collection), liver function tests,prothrombin time-international normalized ratio (PT-INR), and partial thromboplastin time (PTT). Laboratory tests were performed on a weekly base. Toxicities were graded using the WHO criteria. The compliance to therapy was assessed through weekly pill counts in addition to a patient diary and evaluation was according to the criteria of Miller et al. (21).

IDA was provided by Pharmacia Upjohn (Milan, Italy) in powder oral capsules of 1 and 5 mg. Each therapy course was administered for 21 days every 28 days, The starting dose of 1 mg was taken around either 8.30 a.m. or 8.30 p.m. In the subsequent cycles, the dose was increased by 1 mg/day (with the larger dose given in the evening) until disease progression, refusal, or DLT. The 1-mg capsule to be added was given alternatively in the morning or in the evening. Patients had a standard meal 20 min before intake of IDA. Supportive care was administered when necessary. DLT was defined as G4 hematological toxicity or any other toxicity of G3 or higher, and MTD was the dose level at which two DLT events occurred. Antiemetics were used in the presence of vomiting of G2 or higher, whereas hematological growth factors were administered in the presence of G4 hematological toxicity.

To achieve a safe treatment, the protocol was planned to start with a very low dosage but permitting dose escalation within the individual patient to better evaluate cumulative toxicity of IDA and duration of response. We planned to enroll cohorts of five patients at each dose level. The dose was escalated by 1 mg/day only if G2 toxicity was not exceeded. If patients had G3 hematological toxicity, they were re-treated at the same dose level. If a patient experienced DLT, the next 5-patient cohort started at the same dose level (for a total of 10 patients), and the patient who had developed DLT was re-treated at 50%of the dose level. If two patients of a cohort of at least five patients experienced DLT, no additional cohort was enrolled and MTD was established.

Patients who needed 2 weeks instead of 1 to recover from toxicity were re-treated at the same dose level. If patients did not recover from toxicity after 2 weeks, they were dismissed from the study. Patients were also dismissed from the study if during the 21 days of IDA intake they had a neutrophil count ≤1,000/μl and/or platelet count≤50,000/μl for >1 week, or cardiac events (congestive heart failure, reduction of LVEF ≥20%). In those cases, patients were replaced with new patients entered at the same dose level. Patients with progressive disease at the end of a specific dose level were taken off the study and replaced with new patients. Assessment of toxicity included all treated patients, whereas only those patients who received at least one 28-day course of IDA were assessable for response.

Blood samples for drug assay were taken on day 21 at 0 (immediately before drug intake), 1, 2, 3, 4, 6, 12, 24, 48, and 72 h after the last oral IDA dose. Blood samples were also collected at 0, 1, 2, 3,and 4 h on day 1, and at 0 h on days 8 and 15. Blood samples were picked up in lithium heparinate tubes and centrifuged immediately;the plasma was stored at −20°C until analysis.

IDA and its metabolite IDOL were measured using a reversed-phase high-performance liquid chromatography method with fluorescence detection, as reported by Zanette et al. (22)with slight modifications. Plasma IDA and IDOL concentrations were quantified using the internal standard method and a calibration curve ranging between 0.10 and 10 ng/ml. The limit of quantification was 0.10 ng/ml. Doxorubicin was used as the internal standard within this range of concentrations. The within- and between-day precision was <10% (as the coefficient of variation) for both IDA and IDOL.

Pharmacokinetic parameters were calculated using a noncompartmental model. Estimates of pharmacokinetic parameters and the numerical validation of the model were obtained by the PCNONLIN 4.0, a nonlinear regression program. The C_max and corresponding time to maximum concentration were determined from the experimental data. AUC was calculated by the trapezoidal rule from time 0 to 12 h (AUC_{0–12 h}). AUC_{0–24 h} was obtained by multiplying AUC_{0–12 h} by 2. The apparent CL (CL_app, in liters/h) was calculated as the ratio of daily IDA dose (in micrograms), and AUC_{0–24 h}. t_1/2 (in hours) was determined by regression analysis of the log concentration versus time data in the elimination phase of both the parent compound and its metabolite. The apparent V_d(V_{d app}, in liters) was calculated as the ratio of clearance and elimination rate (in inverse hours),which is the slope of the log-linear terminal phase. CL_app and V_{d app}for IDOL were obtained with the same dose used for IDA calculations. An approximation would be introduced depending on the proportion of absorbed IDA that was not converted to IDOL and on the rate at which the parent drug was converted to its metabolite.

Statistical analysis was performed with software SAS system 6.12, 1989–1995 (SAS Institute Inc., Cary, NC). Correlation between kinetic and dynamic parameters was performed by the linear regression analysis. Regression analysis of multiple parameters against a single variable, to determine independently predictive parameters, was performed using a stepwise regression analysis. The Wilcoxon test was used for statistical evaluation of paired data when two groups of parameters were compared. The significance of the coefficients of the correlation found was determined as reported elsewhere (23).

A total of 69 cycles of treatment with IDA were administered (mean,2.1 ± 1.4; median, 2; range, 1–6; Table 1). Three patients did not complete even a single 21-day therapy cycle. One of them refused to continue therapy after 5 days at 5 mg/day because of psychological problems. The other two patients had neutrophils count <1000/μl for >7 days at the dose level of 7 mg/day and were taken off study on day 17 of therapy. In both patients, neutrophils (≥2000/μl) spontaneously recovered in 1 week.

The toxicities are listed in Tables 2, 3, and 4. Overall, IDA was well tolerated. Hematological toxicity was the most common. Generally, the ANC nadir decreased with the increase in IDA dose with a statistically significant correlation(P = 0.00019; r = −0.44). At the highest dose level of IDA (10 mg/day), the median ANC was 850/μl(min, <100/μl; max, 1500/μl; mean, 870 ± 430/μl). However,a single patient experienced G4 neutropenia at a dose level of 3 mg/day. Such a toxicity occurred when the dose was escalated from 2 to 3 mg/day; to further explore treatment safety, we treated two additional patients at 2 mg/day. Thus, 5 patients had the dose escalated from 2 to 3 mg/day and a total of 10 patients were treated with 3 mg/day. No DLT was observed in these 10 patients.

The mean time to neutrophil nadir was 23.0 ± 4.5 days (median, 21 days; range, 7–58 days). Twenty-two patients had an adequate neutrophil count for recycle (i.e., ≥2000/μl) within 7 days from the end of IDA administration. Seven patients recovered within 2 weeks and thus were re-treated with the same dose: three, one,one, and two patients were re-treated at the dose levels of 6, 7, 9,and 10 mg/day, respectively. Among these patients, two had three cycles(one patient at 6 mg/day and one patient at 10 mg/day, respectively;Table 1). Only two patients did not recover adequate neutrophil counts within 14 days and were dismissed from the study. One of these patients had an ANC nadir of 1000/μl at 7 mg/day and completely recovered from toxicity in 29 days. The other patient had an ANC nadir of 1555/μl at 3 mg/day and recovered in 35 days. Both these patients had been pretreated with chemotherapy (FEC).

One patient developed a G4 hematological toxicity (DLT) at 10 mg/day. The ANC nadir was <100/μl, platelets were <10,000/μl,erythrocytes were 2.07 × 10⁶/μl, and hemoglobin was 6.2 g/dl. Erythrocyte and platelet transfusion, together with granulocyte colony-stimulating factor rescue, was performed. The toxicity resolved completely in 21 days. It must be considered that in this patient’s ANC was 4400/μl on day 14.

Analysis of the neutrophil nadir over multiple courses of IDA showed no evidence of cumulative hematological toxicity.

Concerning nonhematological toxicity, diarrhea occurred in few patients and at doses ≥9 mg/day. (Table 3). G1-G2 diarrhea was observed in four different patients. One patient had G3 diarrhea (DLT) when treated at 10 mg/day. Diarrhea started on day 17 of IDA intake and was maximum on day 21; it needed 1 week for resolution.

Two patients experienced DLT (G4 hematological toxicity and G3 diarrhea) at 10 mg/day, and MTD was defined at this dose level. The median dose intensity at 10 mg/day, as defined by the amount of drug delivered per week, was 44.7 mg (range, 35–52.5 mg; mean, 44.9 ±7.5 mg).

One patient had a LVEF fall of ∼30%, with bradycardia and hypotension, during the second cycle with IDA at 7 mg/day. However, it should be considered that this patient was concomitantly treated with radiotherapy in the mediastinum (5000 rads). Despite the previous,large doses of anthracyclines, no additional patient had cardiovascular toxicity. The median LVEF was 62.5% (range, 40–67%; mean, 61 ±7.1%) with no significant (P not significant by Wilcoxon test) difference with the basal value.

An attempt to calculate toxicities versus IDA dose expressed in mg/m²/day instead of mg/day was made. The results are shown in Table 4. The two patients that experienced DLT at the dose of 10 mg/day received an IDA dose >5.5 mg/m²/day. The G4 hematological toxicity occurred in a patient treated with 6.85 mg/m²/day IDA, and the G3 diarrhea was observed in a patient treated with 5.65 mg/m²/day IDA. Overall, in our study, four patients (for a total of five courses) had an IDA dose of >5.5 mg/m²/day. All of these patients were in the cohort of five patients treated with 10 mg/day IDA.

The response evaluation was performed in 21 patients. A partial response was observed in three patients (14.3%) treated with doses from 2 to 6 mg/day, from 7 to 9 mg/day, and from 8 to 10 mg/day,respectively. The response duration was 3–8 months, and the number of therapy cycles was four to six. These three patients previously had received anthracyclines as postoperative adjuvant treatment and had relapsed 11, 29, and 35 months, respectively, from the end of adjuvant chemotherapy. Six patients (28.6%) had stabilization of disease for 2–6 months (median, 4.0 months). Among these, five patients (83%) had progressed previously with an i.v. epirubicin-containing chemotherapy regimen. Twelve patients (57%) had disease progression. Among these latter, five had early disease progression after the first course of therapy and were dismissed from the study. Finally, 10 patients were not evaluable for response (Table 5).

The pharmacokinetics of IDA and its metabolite IDOL were evaluated in 29 patients during 56 courses of therapy. Analysis was not performed in the patient who refused to continue therapy after 5 days of treatment and in the patient who developed G4 hematological toxicity at the dose of 10 mg/day. Because of the supportive therapy and vomiting, it was not possible to perform adequate sampling collections for pharmacokinetic analysis in this patient. Table 6 summarizes the IDA and IDOL pharmacokinetics as determined by serial blood sampling performed on the last day of IDA administration (day 21) in 27 patients and on day 17 in 2 patients who had no further therapy. Both IDOL and IDA exhibited linear pharmacokinetics over the dose range studied (Fig. 1). The concentrations of IDOL in plasma exceeded those of IDA immediately after the start of treatment and remained higher over the 21 days of treatment (Fig. 1 and Table 7).

The schedule adopted in this study was such to approach an i.v. continuous infusion. With regard to this aspect, intraday fluctuations{[(C_max −C_min)/C_max] × 100}between IDA concentrations immediately before the last capsule of IDA(C_min), when drug plasma concentrations were at the lowest level, and after the last capsule(C_max), i.e., at the peak, were 41.0 ± 15.3%, (median, 44.0%; range, 15.8–62.0%; Fig. 2). Intraday variations of IDOL were 19.3± 9.4% (median, 18.0%; range, 9.9–40.9%). Sampling performed on days 8, 15, and 21 indicated that both IDA and IDOL maintained a relatively constant steady-state levels throughout the course of drug administration (Table 7).

Systemic clearance remained constant over the dose range investigated. The IDA/IDOL AUC ratio was not dose-dependent, suggesting that the formation of IDOL is not a relating step of IDA elimination(Table 6). A highly significant correlation was observed between IDA AUC and IDOL AUC (P < 0.000001; r =0.83).

No evidence of accumulation of plasma IDA and IDOL and no significant differences in IDA and IDOL AUC occurred during subsequent cycles with the same dose level in the six patients investigated. In a single patient treated with 2 and 3 mg/day, the plasma level of IDOL was ∼6-fold higher than the median value. The IDOL AUC was 152.2 and 201.7 μg·h/liter at the doses of 2 and 3 mg/day, respectively,whereas the IDA AUC was within the range observed in the other patients treated with the same doses. This patient had severe G4 neutropenia at the dose of 3 mg/day and was dismissed from the study because of disease progression. She was receiving, in addition to IDA, quinidine,paracetamol, codeine, and diclofenac.

A relationship between plasma IDA and IDOL and toxicity was investigated. By univariate analysis, significant associations (Fig. 3) were observed between ANC at nadir and IDA AUC (P = 0.022; r = −0.33), IDA C_max (P = 0.0067; r = −0.38), IDOL AUC (P = 0.0009; r = −0.43), and IDOL C_max(P = 0.0016; r = −0.41). By stepwise linear regression multivariate analysis that included the IDA AUC, IDOL AUC, IDA C_max, and IDOL C_max in the model, the strongest and only significant determinant of ANC was IDA C_max. However, it accounted for only ∼14% of ANC variance(P = 0.01; R² = 0.14). By univariate analysis, significant associations between ANC at nadir and IDA CL_app (P = 0.0018; r = 0.48) were also observed.

Finally, The AUC for IDA or IDOL showed no correlation with creatinine,bilirubin, albumin, aspartate aminotransferase, alanine aminotransferase, and γ-glutamyltransferase, respectively, or with performance status and patient age.

In this dose escalation study of chronic oral drug administration,IDA was generally well tolerated. Neutropenia was the predominant toxicity. Generally, myelosuppression became more severe as the dose was escalated, and significant associations were observed between ANC at nadir and dose level. Neutropenia was most prominent as patients approached day 21 of therapy, and the treatment was discontinued in two patients on day 17 because of an ANC <1000/μl. However, ANC abnormalities were not related solely to the dose, as indicated by the G4 neutropenia toxicity observed in a single patient treated with 3 mg/day. Therefore, the possibility of an individual’s predisposition to develop toxicity with this administration schedule should be considered.

The predominant nonhematological toxicity was diarrhea. However, it was generally mild, in agreement with a previous study (4) in which IDA produced severe or moderate diarrhea only in ∼5% of patients. Diarrhea was strictly dose dependent and was observed only at a dose ≥9 mg/day in 3 of 10 patients.

We determined the MTD of IDA in this schedule to be 10 mg/day. Neutropenia and diarrhea were the DLTs. The two patients that experienced DLT at the dose level of 10 mg/day received an IDA dose>5.5 mg/m²/day. This represents a 2–3-fold enhancement of dose intensity compared with the standard schedule of oral IDA administration (30–45 mg/m² every 3 weeks). The clinical toxicity/dose relationship for this schedule appears to be steep, and dramatic increases in toxicity were observed when passing from 9 to 10 mg/day or when using IDA doses >5.5 mg/m²/day, although the percentage of difference between these dosages is little. Therefore, caution has to be observed when doses approximate the total dose/day MTD or 5.5 mg/m²/day. On the basis of these findings, we believe that a total dose of 8 mg/day (4 mg every 12 h for 21 days every 28 days) with a dosage <5 mg/m²/day could be given safely with this schedule, and it could represent the recommended phase II study dose.

In our study, hospitalization was required only for the patients who developed DLTs; with these exceptions, no hematological growth factors or antiemetics were required. Generally, patients recovered adequate neutrophil counts (≥2000/μl) for recycle within 1 week, and only two patients were dismissed from the study for inadequate neutrophil count for >2 weeks. Concerning cardiac adverse events, chronic IDA administration was safe. This was probably due to the lower cardiotoxicity of IDA compared with other anthracycline analogues (12) and to the prolonged continuous administration (24). Concerning the reduction of ∼20% in LVEF observed in one patient, this must be ascribed to an extenuating circumstance(concomitant salvage-radiotherapy with 5000 rads in the mediastinum).

In the clinical practice, drug dose is calculated as a function of body-surface area, but recently this method has been questioned (25). Moreover, because of the standard commercial formulation of oral antineoplastic drugs, it is difficult to adapt the precise dosage to the body surface area. In the present study, we used the IDA dose per day instead of dose/m²/day because previously reported data on oral IDA suggested a great variability in the bioavailability (10) and such variations in bioavailability could be greater than interpatient variations in body surface. However, we also investigated the relationship between toxicity and daily dose adjusted to the body surface area. In particular, the finding that MTD occurred in patients treated with an IDA dose >5.5 mg/m²/day strongly suggests that this dose/m²/day represents the limit for MTD.

The intrapatient dose escalation adopted in this study does not allow definitive conclusions about cumulative toxicity for a specific dose level. However, cumulative IDA exposure does not appear to be a predisposing factor to myelosuppression because toxicity was not related to the number of cycles administered to each patient. No patient re-treated with the same dose level developed cumulative toxicity, and in addition, the two DLTs were observed during the first course of IDA.

After chronic oral IDA administration, the pharmacokinetic parameters of IDA and IDOL (t_1/2, CL, and V_d) were consistent with those described previously (26), assuming a bioavailability of∼10–30% for IDA and a metabolized amount of ∼80% for IDOL (27). The plasma levels of IDOL rapidly exceeded those of the parental compound and remained higher throughout the treatment,indicating a substantial first-pass conversion of IDA to IDOL during absorption from the gastrointestinal tract. The ratio IDOL/IDA AUC was stable across the dose range, suggesting that reduction of IDA to IDOL by aldoketoreductase was not saturated with the schedule used in this study.

The AUCs for IDA and IDOL showed interpatient variations at selected dose levels. However, the IDA and IDOL AUCs generally showed a good correlation. We think that this could reflect interpatient variations in IDA absorption rather than IDA metabolism, as also suggested by Schleyer et al. (27). On the contrary,individual abnormalities in IDA metabolism should be considered a very rare event with chronic oral IDA administration because only one patient had an IDOL/IDA ratio ∼6-fold higher than that observed in the remaining patients. The abnormal IDOL plasma level in this patient was associated with increased IDOL t_1/2 and reduced IDOL CL_app. The liver function test and creatininemia for this patient were within the normal range, and at present, we cannot conclude that some drugs taken by this patient (i.e.,quinidine) during IDA therapy may have influenced the elimination pathway of IDOL. Quinidine is a substrate for P-gp and could compete with IDOL. P-gp is expressed in the liver at the luminal surfaces of bile canaliculi (28) and probably facilitates the biliary excretion of IDOL more than IDA, whose transport is less affected by P-gp activity (15).

At present, few data are available regarding the relationship between oral IDA pharmacokinetics and toxicity (5, 13, 29). We found that the nadir granulocyte count correlated, by univariate analysis, with the IDA AUC, IDOL AUC, IDA C_max,and IDOL C_max. This strict association could suggest that even the interpatient variability observed in the plasma drug level at selected dose levels is of clinical interest. Multivariate regression analysis identified IDA C_max as the strongest determinant of ANC at nadir and the most significantly predictive variable independent from IDOL C_max, IDA C_max, IDOL AUC,and IDA AUC, which were entered into the stepwise regression equation. However, IDA C_max accounted for only ∼14% of variance of ANC, and this does not allow definitive conclusions on the identification of the best variable for the prediction of IDA myelosuppression. Nevertheless, the pharmacodynamic correlations indicate that hyperfractionated oral IDA, by reducing the plasma IDA C_max, could contribute to reduced hematological toxicity.

This study was not intended to demonstrate an effectiveness of hyperfractionated oral IDA in breast cancer. However, 3 of the 21 patients (14.3%) evaluable for response did have objective responses,and 6 patients (28.6%) showed stable disease. These results could be promising for further phase II studies. The limited sample size precluded conclusions regarding a relationship between response and dose.

In conclusion, chronic oral administration of IDA is easily administered and well tolerated by outpatients. This schedule allows greater dose intensity compared with conventional schedules, and IDOL appears to have some pharmacological effects. Whether chronic oral IDA administration offers advantages over a conventional schedule will require formal phase II studies. However, the activity and toxicity profiles of IDA observed with this schedule may be promising.

We thank Prof. G. Cartei for useful comments on the manuscript.