Ifosfamide in combination with paclitaxel or doxorubicin - Nature

Bone Marrow Transplantation, (1999) 23, 427–435  1999 Stockton Press All rights reserved 0268–3369/99 $12.00 http://www.stockton-press.co.uk/bmt

Ifosfamide in combination with paclitaxel or doxorubicin: regimens which effectively mobilize peripheral blood progenitor cells while demonstrating anti-tumor activity in patients with metastatic breast cancer HM Prince1, J Gardyn1, MJ Millward1, D Rischin1, P Francis1, P Gates1, P Chapple1, M Quinn1, S Juneja1, M Wolf1, EH Januszewicz1, G Richardson2, J Scarlett2, P Briggs2, M Brettell1 and GC Toner1 1 2

Blood and Marrow Transplant Service, Division of Haematology and Medical Oncology, Peter MacCallum Cancer Institute; and Department of Medical Oncology and Clinical Haematology, Monash Medical Centre, Melbourne, Victoria, Australia

Summary: For patients with metastatic breast cancer (MBC) who undergo high-dose therapy with autologous peripheral blood progenitor cell (PBPC) transplantation, an important prerequisite is a mobilization regimen that efficiently mobilizes PBPCs while producing an effective anti-tumor effect. We prospectively evaluated ifosfamide-based chemotherapy for mobilization efficiency, toxicity and disease response in 37 patients. Patients received two cycles of the ifosfamide-based regimen; ifosfamide (5 g/m2 with conventional-dose cycle and 6 g/m2 with mobilization cycle) with either 50 mg/m2 doxorubicin (if limited prior anthracycline and/or progression more than 12 months after an anthracyclinebased regimen) or 175 mg/m2 paclitaxel. For the mobilization cycle, all patients received additional G-CSF (10 ␮g/kg SC, daily) commencing 24 h after completion of chemotherapy. The target yield was ⬎6 × 106 CD34+ cells/kg, sufficient to support the subsequent three cycles of high-dose therapy. The mobilization therapy was well tolerated and the peak days for peripheral blood (PB) CD34+ cells were days 10–13 with no significant differences in the PB CD34+ cells mobilization kinetics between the ifosfamide-doxorubicin vs ifosfamide-paclitaxel regimens. The median PBPC CD34+ cell content ranged from 2.9 to 4.0 × 106/kg per day during days 9– 14. After a median of 3 (range 1–5) collection days, the median total CD34+ cell, CFU-GM and MNC for all 44 individual sets of collections was 9.2 × 106/kg (range 0.16–54.9), 37 × 104/kg (range 5.7–247) and 7.3 × 108/kg (range 2.1–26.1), respectively. The PBPC target yield was achieved in 35 of the 37 patients. The overall response rate for the 31 evaluable patients was 68% with 10% having progressive disease. Thirty-three patients have subsequently received high-dose therapy consisting of three planned cycles of high-dose ifosfamide, thiotepa and paclitaxel with each cycle supported Correspondence: Dr HM Prince, Division of Haematology and Medical Oncology, Peter MacCallum Cancer Institute, Locked Bag 1, A’Beckett St, Melbourne 3000, Victoria, Australia Received 22 May 1998; accepted 16 October 1998

with PBPCs. Rapid neutrophil and platelet recovery has been observed. Ifosfamide with G-CSF in combination with doxorubicin or paclitaxel achieves effective mobilization of PBPC and anti-tumor activity with minimal toxicity. Keywords: ifosfamide; paclitaxel; doxorubicin; mobilization; stem cells

The value of dose-intensive chemotherapy in metastatic breast cancer (MBC) continues to be debated1–4 and highdose chemotherapy with autologous bone marrow (ABM) or peripheral blood progenitor cell (PBPC) transplantation continues to be investigated.5 A single small randomized study examining the outcome of patients with MBC treated with high-dose chemotherapy and ABM or PBPC support demonstrated superior response rates, complete responses (CR) and overall survival (OS) for patients treated in the high-dose arm.6 Furthermore, in heavily pre-treated patients, CR rates of 20–64% have been reported using a single cycle of high-dose chemotherapy with PBPC transplantation.7 Despite these promising results, only a minority (approximately 10–25%) of these highly selected groups of women with MBC experience prolonged progression-free survival following high-dose therapy.5 We were therefore interested in examining the tolerability and efficacy of a novel approach utilizing repetitive high-dose combination chemotherapy for patients with MBC. We initiated a phase I/II study in heavily pre-treated patients with MBC using three cycles of high-dose ifosfamide, thiotepa and paclitaxel, with each cycle supported by PBPCs. An important prerequisite for this therapy, was a reliable method of obtaining sufficient PBPCs to ensure rapid and durable engraftment. Furthermore, an effective mobilization regimen needed not only to mobilize adequate PBPCs, but also potentially achieve an anti-tumor effect to maintain patients in at least a stable disease state at the time of commencing the high-dose phase of therapy. We selected ifosfamide as the ‘back-bone’ for our mobilization regimen for a number of reasons. Firstly, ifosfamide can be incorporated into chemotherapy regimens to mobilize PBPCs.8–14 Secondly, ifosfamide has some potential

Ifosfamide mobilization in breast cancer HM Prince et al

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Table 1

Patient characteristics (n = 37) All

Ifosfamide-doxorubicin

Ifosfamide-paclitaxel

37

24

13

15 2 15a 5 37 7 44

15 2 4 3 22 4 26

0 0 11 2 12 2 14

3 1 4

44 (23–58)

44 (23–56)

44 (38–58)

43 (29–50)

Mobilization regimen (patients) Disease status pre-ifosfamide-based chemotherapy Sensitive Stable Resistant Not evaluable 1st mobilisation regimen 2nd mobilisation regimen Total Median age (range) Locally advanced Metastatic nodal liver bone marrow lung brain skin peritoneum ovary adrenal Median No. met sites Median No. of prior regimens Median No. of prior chemotherapy cycles No. of patients with prior cyclophosphamide No. of patients with prior taxanes No. of patients with prior RT for bone mets

2 2 7 30 11 5

3 34 17 13 17 7 12 1 2 2 2 1 (1–4) (1–3) (1–15) (81%) (30%) (14%)

1 6 15 2 1

(1–3) (1–15) (63%) (8%) (4%)

2 8 13 7 7

(1–3) (1–15) (100%) (54%) (15%)

G-CSF

3 9 4 2 2

(1–3) (7–15) (100%) (50%) (50%)

a Four patients with refractory disease were not evaluable for response to ifosfamide-based chemotherapy (see text). RT = radiotherapy.

advantages over cyclophosphamide. Pre-clinical studies have demonstrated that the unique structural properties of ifosfamide may have a beneficial anti-tumor activity; ifosfamide is an analogue of cyclophosphamide with translocation of a chlorethyl group which provides a more effective DNA cross-linking distance between two independent functional alkylating moieties.15,16 Pre-clinical studies demonstrate differences in alkylation kinetics between the two active metabolites, phosphoramide mustard and isofosforamide mustard. This should result in longer survival of isofosforamide mustard within the cell cytoplasm and an increased probability of reaching the nucleus and alkylating DNA.17 These findings have been supported by the demonstration that ifosfamide has superior anti-tumor activity in some cell lines.18,19 Thirdly, in clinical studies, ifosfamide has demonstrated efficacy in advanced breast carcinoma.16,20–23 Although to date there is no conclusive evidence that ifosfamide is superior to cyclophosphamide in the treatment of breast cancer, taken together, we believed it rational to use ifosfamide-based mobilization in our cohort of heavily pre-treated patients. We selected either doxorubicin or paclitaxel in combination with ifosfamide depending on prior anthracycline exposure. Doxorubicin-containing regimens are well documented as achieving effective mobilization of PBPCs in breast cancer.24,25 However, we anticipated that a number of patients in this prospective study may have been heavily pre-treated and at risk of cardiac toxicity, and/or had pro-

gressed after a recent anthracycline. Therefore, in these patients paclitaxel was substituted for doxorubicin. Furthermore, paclitaxel can achieve 20–30% objective responses in anthracycline-resistant patients,26,27 with evidence that it may enhance PBPC yields.28–30 Here, we report on ifosfamide with doxorubicin or paclitaxel for mobilization of PBPCs in heavily pre-treated patients with MBC. We sought to determine if these ifosfamide combinations were tolerable and effective regimens in such patients, while offering a reliable method for obtaining adequate PBPCs to support multiple cycles of high-dose therapy.

Materials and methods Patient characteristics Patients with histologically and/or cytologically proven metastatic or locally advanced breast cancer were prospectively entered into a phase I/II clinical trial utilizing three cycles of high-dose ifosfamide, thiotepa and paclitaxel (see below) with each cycle supported with PBPCs. Sufficient PBPCs to support three cycles of high-dose therapy were collected prior to any of the cycles of high-dose therapy. Patients were excluded if they had a history of ventricular arrhythmia, myocardial infarction 6 months prior to enrollment, congestive heart failure, sensitivity to any of


the study drugs, were pregnant or lactating, had an ECOG performance status ⬎2, life expectancy of less than 2 months, absolute neutrophil count (ANC) ⬍1.5 × 109/l, platelet count ⬍100 × 109/l, bilirubin ⬎1.5 times upper limit of normal, aspartate transaminase ⬎2 times upper limit of normal, albumin ⬍34 g/l or creatinine ⬎1.5 times upper limit of normal. Written informed consent was obtained from all patients and the protocol was approved by the Institutional Ethics Committee of Peter MacCallum Cancer Institute. Chemotherapy Patients entered on the study received two cycles of ifosfamide-based chemotherapy, the mobilization cycle was administered using a higher dose of ifosfamide with GCSF. The chemotherapy regimen was determined by prior cumulative anthracycline exposure or time between the last anthracycline treatment to disease progression; patients with a cumulative dose of doxorubicin exceeding 250 mg/m2 (or equivalent) or those who had progressed within 12 months of receiving an anthracycline-based regimen, received a mobilization regimen of ifosfamidepaclitaxel. All other patients received an ifosfamidedoxorubicin regimen. For the first cycle of chemotherapy patients received ifosfamide (Holoxan; Asta Medica Australasia Pty Ltd, Sydney, Australia) at a dose of 5 g/m2 as a 24 h continuous infusion (day 1). Mesna (Uromitexan; Asta Medica Australasia Pty Ltd) was administered at 1 g/m2 intravenous bolus over 30 min prior to the ifosfamide infusion, followed by 5 g/m2 (combined with the ifosfamide) and administered over 24 h. Following completion of the ifosfamide/mesna infusion, mesna (1 g/m2) was infused over 6 h or 2 g/m2 of oral mesna administered in two divided doses. Doxorubicin at 50 mg/m2 was administered intravenously on day 1 prior to the ifosfamide. Paclitaxel (Anzatax; FH Faulding Pharmaceuticals, Adelaide, Australia) was administered as a 3 h infusion of 175 mg/m2 on day 2, at least 3 h following completion of ifosfamide. No sedative hypnotics were administered during the ifosfamide infusion. No hematopoietic growth factors were given following this phase of chemotherapy. On approximately day 21, patients received mobilization chemotherapy consisting of the same drugs except that the ifosfamide dose was increased to 6 g/m2 and administered with mesna (1.2 g/m2) bolus followed by 6 g/m2 24 h infusion and 1.2 g/m2 post infusion. Doxorubicin and paclitaxel doses were the same. Granulocyte colony-stimulating factor (G-CSF: Neupogen; Amgen Australasia Pty Ltd) was commenced 24 h after completion of mobilization chemotherapy at 10 ␮g/kg subcutaneously daily and continued until the last day of apheresis. Four patients received GCSF (10 ␮g/kg) alone for mobilization of PBPCs. In three of these patients, G-CSF mobilization was chosen first because of prior extensive chemotherapy exposure. In each case it was unsuccessful and was followed by an ifosfamide-based mobilization regimen. In one patient mobilization with G-CSF alone was utilized after an inadequate collection following the ifosfamide-doxorubicin mobilization regimen.

Disease assessment Patients had disease assessment prior to their first cycle of ifosfamide-based chemotherapy and prior to their first cycle of high-dose therapy. Disease status was determined by complete physical examination, chest X-ray, computerised tomography (CT) of abdomen and thorax, isotope bone scan, CA 15–3, and bone marrow biopsy (repeated only if originally positive). As a means of attempting to identify a patient’s potential response to ifosfamide-based chemotherapy, patients were classified as sensitive or resistant to prior chemotherapy. Patients with a complete response (CR) or partial response (PR) were defined as having chemotherapy-sensitive disease. Patients with progressive or stable disease following the last cycle of chemotherapy were defined as having resistant disease. Patients were evaluable for response to subsequent ifosfamide-based chemotherapy if they had bi-dimensionally measurable disease. Patients were not evaluable for response if complete surgical resection of tumor was performed prior to ifosfamidebased chemotherapy or if bone lesions detectable by radionucleotide bone scans were the sole evidence of disease. Response to subsequent ifosfamide-based therapy was defined as follows: CR was defined as the total disappearance of all reversible clinical evidence of disease. Partial response was defined as at least a 50% reduction in the size of all measurable tumor areas as measured by the perpendicular diameters of the greatest length and width. Because patients proceeded immediately to high-dose therapy, response could not be followed for 4 weeks, nor could response duration be evaluated. Progressive disease (PD) was defined as the appearance of a new lesion, or an increase of 25% in the sum of areas of lesions within any organ site. Stable disease (SD) was defined as disease that fails to qualify for either a response or progressive disease. Apheresis procedure Patients had a routine full blood examination on day 8 following mobilization. Daily CD34+ cell enumeration of the peripheral blood (PB) was commenced when the absolute neutrophil count (ANC) reached 0.5 × 109/l following the nadir. Apheresis was initiated when the PB CD34+ cell count exceeded 0.5 × 107/l.31 By employing this trigger point for initiating apheresis, patients were harvested 8–16 days following mobilization. For patients mobilized with G-CSF alone (n = 4), apheresis was commenced on day 5. Apheresis was performed using a Haemonetics V50, CS3000plus (Baxter Healthcare Corp, Deerfield, IL, USA) or Spectra (Cobe, Denver, CO, USA) cell separators. Blood was collected via a central venous access device or from peripheral veins with 1.5–2.5 times the patient’s estimated blood volume processed. Apheresis was continued until sufficient cells to support three separate cycles of high-dose therapy, had been collected, ie a minimum target of 6 × 106/kg (= 3 cycles of high-dose therapy, each with a minimum of 2 × 106/kg CD34+ cells). To ensure uniformity, each collection was divided into three separate bags, so that each re-infusion contained PBPCs collected from each day of apheresis. Repeat PBPC collection was performed if the initial set of collections was deemed inadequate (ie initial

429


430

100.00

PB CD34 × 107/l

10.00

1.00

0.10

0.01 D8

D9

D10

D11

D12

D13

D14

D15

D16

D14 3 2.2 6.1 73 27

D15 6 0.63 1.8 7.3 2.5

D16 4 0.47 1.1 7.6 2.6

Days after mobilization n min median max mean

D8 6 0.01 0.01 8.0 2.3

D9 28 0.01 0.46 17 4.0

D10 32 0.01 5.6 48 9.7

D11 34 0.01 5.5 21 7.4

D12 25 0.21 10.0 21 9.8

D13 11 0.23 3.4 51 9.1

Figure 1 The PB CD34+ cell counts (log scale) following mobilization with the ifosfamide-based regimens (n = 40). Median values represented by horizontal lines.

total collection ⬍6 × 106/kg). In patients with a borderline collection according to CD34+ cell criteria (ie 4.5– 6.0 × 106/kg), an autograft was deemed acceptable if the total colony-forming units granulocyte–macrophage (CFUGM) exceeded a total of 20 × 104/kg.

served PBPC were thawed and infused on day 0. All patients received G-CSF (5 ␮g/kg/day) subcutaneously from day 1 until the ANC was ⬎1.5 × 109/l for 3 consecutive days. All patients received prophylactic ciprofloxacin, aciclovir and ranitidine.

Cell enumeration, processing and cryopreservation

Statistical analysis

Determination of PB and PBPC cell counts including WCC, MNC and CD34+ cells has been previously described.31 The autograft content of MNC, CD34+ cells and CFU-GM (per kg body weight) was determined using the patient’s actual body weight. As described, to ensure uniformity, the product from each day of collection was equally divided into three separate bags, cryopreserved in 10% DMSO and stored in vaporphase liquid nitrogen. Each re-infusion was equivalent and contained PBPCs collected from each day of apheresis.

Spearman correlation was used to compare PB CD34 and PBPC CD34 values. The Mann–Whitney U test was used to compare the influence of the ifosfamide-doxorubicin and ifosfamide-paclitaxel mobilization regimens on the PBPC CD34, CFU-GM and MNC, and ANC and platelet recovery following high-dose therapy. Fisher’s exact test was used to compare the doxorubicin- and paclitaxel-containing regimens on response rate. All results are expressed as twosided P values. Statistical analysis was performed using GraphPad Prism Ver 2.01 and GraphPad StatMate, Ver 1.00 for Windows 3.1. (GraphPad Software, San Diego, CA, USA).

High-dose therapy Prior to mobilization, patients were enrolled in a phase I/II study of high-dose ifosfamide (7.5–12.5 g/m2/cycle), thiotepa (200–350 mg/m2/cycle) and conventional-dose paclitaxel (175 mg/m2/cycle).32 High-dose therapy was administered according to the following schedule; on day −4 patients received mesna (20% w/w of the ifosfamide dose) over 30 min followed immediately by a 24 h infusion of ifosfamide with an equivalent dose of mesna. Immediately following the ifosfamide/mesna infusion, mesna (20% w/w of the ifosfamide dose) was administered intravenously over 8 h. Thiotepa was administered in equally divided doses on days −4 to −2, inclusive. Paclitaxel (175 mg/m2) was administered as a 3 h infusion on day −2. Cryopre-

Results Patient characteristics Patient characteristics are summarized in Table 1. Thirtysix females and one male with the median age of 44 (range 23–58 years) underwent PBPC collection. The majority of patients had metastatic disease (n = 34) and three had locally advanced disease. Most patients were heavily pretreated and 15 were resistant to conventional-dose chemotherapy, the majority of whom received the paclitaxelcontaining regimen (Table 1).


431

a 100.00

PB CD34 × 107/l

10.00

1.00

0.10

0.01

D8

D9

D10

D11

D12

D13

D14

D15

D16


D8 2 0.01 0.01 0.01 0.01

D9 18 0.01 0.10 16.5 4.0

D10 20 0.01 4.77 48.3 9.7

D8

D9

D10

D11 23 0.01 7.57 20.5 8.1

D12 21 0.21 12.1 20.9 10.4

D13 11 0.23 3.4 50.7 9.11

D14 2 6.08 39.6 73.2 39

D15 5 0.63 1.85 7.27 2.68

D16 4 0.47 1.14 7.6 2.58

D11

D12

D13

D14

D15

D16

D14 1 2.20 2.20 2.20 2.20

D15 1 1.70 1.70 1.70 1.70

D16 0

b 100.00

PB CD34 × 107/l

10.00

1.00

0.10

0.01


D8 4 0.01 3.03 7.98 3.51

D9 10 0.01 2.39 13.5 4.89

D10 12 0.50 6.18 30.0 9.72

D11 11 2.17 5.27 12.8 5.99

D12 4 3.40 6.91 11.2 7.10

D13

Figure 2 The PB CD34+ cell counts (log scale) following mobilization with (a) the ifosfamide-doxorubicin regimen (n = 26) and (b) the ifosfamidepaclitaxel regimen (n = 14). Median values represented by horizontal lines.

Apheresis collections All 37 patients underwent mobilization with an ifosfamide based-regimen. Of these, seven patients had an additional mobilization and collection with either the same regimen or G-CSF alone (Table 1). Consequently, the total data set includes the results of 44 mobilizations and collections with 133 individual apheresis procedures. Once the PB ANC exceeded 0.5 × 109/l (on or after day

8 in all cases) the PB CD34/l was determined. If the PB CD34+ cells exceeded 0.5 × 107/l, apheresis was performed. Indeed, we have previously reported the value of this PB CD34+ cell threshold; the strong correlation between PB CD34+ cell and the PBPC CD34+ cell content was confirmed in this study (Spearman correlation; r = 0.8854, P ⬍ 0.0001).31 The peak days for PB CD34+ cells were days 10–12 (Figure 1). There was no significant difference in the PB CD34+ cell mobilization kinetics between ifos-


432

100.00

PB CD34 × 106/kg

10.00

1.00

0.10

0.01

D8

D9

D10

D11

D12

D13

D14

D15

D16

D14 3 0.61 3.0 23.0 8.7

D15 6 0.58 0.76 5.9 1.7

D16 4 0.15 1.1 4.5 1.7


D8 2 1.54 2.98 4.41 2.98

D9 14 0.01 3.7 12.0 4.6

D10 25 0.28 3.6 18.0 5.4

D11 31 0.55 4.0 12.0 4.6

D12 24 0.01 4.0 16.0 5.2

D13 10 0.72 2.9 25.0 6.1

Figure 3 The peripheral blood progenitor cell (PBPC) CD34+ cell content (log scale) following mobilization with the ifosfamide-based regimen (n = 40). Median values represented by horizontal lines.

famide-doxorubicin vs ifosfamide-paclitaxel (day 9, P = 0.1191; day 10, P = 0.4715; day 11, P = 0.8540; day 12, P = 0.3940) (Figure 2). Using the above criteria, the median day to initiate PBPC harvesting was day 10 (range 8–13; s.d. = 1.15). The median PBPC CD34+ cell content ranged from 2.9 to 4.0 x 106/kg per day during days 9–14 (Figure 3). Following a median of 3 days (range 1–5) collection for each patient following each mobilization, the median total CD34+ cell, CFU-GM and MNC for all 44 individual sets of collections was 9.2 × 106/kg (range 0.16–54.9), 37 × 104/kg (range 5.7–247) and 7.3 × 106/kg (range 2.1–26.1), respectively. There were no significant differences in total PBPC autograft yields between the mobilization regimens of ifosfamide-doxorubicin vs ifosfamide-paclitaxel; CD34+ cells (P = 0.059), CFU-GM (P = 0.156) and MNC (P = 0.550). All patients were planned to receive subsequent repetitive high-dose ifosfamide, thiotepa and paclitaxel. As described, each of three high-dose cycles was followed by PBPC support each with a target CD34+ cell autograft count of 2 × 106/kg, thus the goal of the mobilization prior to this high-dose phase was to achieve a CD34+ cell yield of greater than 6 × 106/kg which was divided equally into three separate bags. Utilizing an ifosfamide-based mobilization regimen we were able to achieve this CD34+ cell target in 33 of the 37 patients (89%). Of the four patients failing to achieve this threshold, two of these patients had a CFU-GM yield of ⬎20 × 104/kg (CD34 × 106/kg were 3.7 and 5.1) and subsequently underwent autotransplant. The two remaining patients had poor CD34+ cell and CFU-GM yields and did not undergo autotransplant. Seven patients underwent a second mobilization and collection because of an inadequate primary collection. The yield of these second collections was generally poor and a

second collection was unlikely to succeed if the first collection had failed (data not shown). Toxicity and responses to mobilization chemotherapy The mobilization therapy was generally well tolerated. One patient developed a grade II acute brain syndrome 12 h after commencing ifosfamide. A CT scan of brain was normal and the patient received three doses of methylene blue with progressive resolution of symptoms over 48 h. No patient developed hemorrhagic cystitis. Hematopoietic parameters following mobilization are detailed in Table 2. The neutrophil nadir was lower in Table 2

Haematopoietic toxicity Ifosfamidedoxorubicin

Mobilization phase Nadir ANCa (×109/l) Nadir plateletsb (×109/l) Transplant phase (n = 84 cycles) ANC ⬎0.5 × 109/l ANC ⬎1.0 × 109/l Platelets ⬎20 × 109/l Platelets ⬎50 × 109/l Platelets ⬎100 × 109/l

Ifosfamidepaclitaxel

0.2 (0.01–1.89) 0.88 (0.11–1.67) 56 (11–139) 108 (30–308)

10d (7–19) 10d (8–20) 13d (9–25) 18d (10–33) 24d (10–152)

10d 11d 14d 22d 30d

(8–26) (9–28) (10–38) (11–40) (16–124)

P value

0.0320 0.0062

0.1345 0.0830 0.0862 0.0062 0.0840

a Full blood counts were performed on day1 and on and after day 8 routinely. Nadir values that may have occurred prior to day 8 cannot be represented therefore these results may not reflect the true nadir counts. b Platelet nadirs universally occurred during apheresis. Two patients developed platelets ⬍20 × 109/l and neither required platelet transfusions.


patients mobilized with the ifosfamide-doxorubicin regimen, however, as blood counts were performed on or after day 8 only, this may not reflect the true nadir in all cases. No patients developed febrile neutropenia. Platelet nadirs universally occurred during the period patients were undergoing apheresis and were also lower in the ifosfamide-doxorubicin group. Only two patients (both in the ifosfamide-doxorubicin group) developed thrombocytopenia below 20 × 109/l and neither required platelet transfusions. No patients required red blood cell transfusions. Thirty-one patients were evaluable for response with bidimensionally measurable disease. Four patients with refractory disease were not evaluable at time of entry into the study; three patients had had locally advanced disease, failed to achieve a response to conventional-dose therapy and subsequently underwent complete surgical resection. A further patient had a soft tissue and bone recurrence, failed to respond to an anthracycline and received local RT. The overall response rate following the mobilization chemotherapy for the 37 patients (including six patients with nonevaluable disease) was 57%, with an additional 19% of patients having stable disease (Table 3). The response rate for the 31 evaluable patients was 68%, 23% having stable disease and 10%, progressive disease. Two patients were excluded from subsequent high-dose therapy because of progressive disease and deteriorating performance status (brain and liver metastases). All 15 patients with chemotherapy-responsive disease prior to the mobilization chemotherapy had a further response (three CRs, 12 PRs). Of the 15 patients who had disease resistant to conventional-dose chemotherapy prior to entry into the study (four patients with non-evaluable disease), there was an 18% (2/11) PR rate with six (55%) having stable disease and three (27%) progressive disease. There was a statistically significant difference in response rates between the ifosfamide-doxorubicin (n = 24) and the ifosfamide-paclitaxel groups (n = 13) (75% vs 23%; P = 0.0046). The result was similar when only evaluable patients (n = 31) were examined (P = 0.0152). However, the pre-treatment characteristics in the paclitaxel group were substantially worse (Table 1). High-dose therapy Of the 37 patients undergoing PBPC collections, 33 patients subsequently received high-dose therapy and PBPC transTable 3 Response rate for all patients following mobilization chemotherapy (n = 37)

n Response rates CR PR SD PD NE RR (total) RR (evaluable)

All (%)

Ifosfamidedoxorubicin (%)

Ifosfamidepaclitaxel (%)

37

24

13

4 (11%) 17 (46%) 7 (19%) 3 (8%) 6 (16%) 21/37 (57%) 21/31 (68%)

4 (17%) 14 (58%) 4 (17%) 0 (0%) 2 (8%) 18/24 (75%) 18/22 (82%)

0 (0%) 3 (23%) 3 (23%) 3 (23%) 4 (31%) 3/13 (23%) 3/9 (33%)

SD = stable disease; PD = progressive disease; NE = not evaluable.

plantation as part of the phase I/II study.32 Twenty-one of these patients were mobilized with ifosfamide-doxorubicin and 12 with ifosfamide-paclitaxel. Of the four patients not undergoing high-dose therapy and PBPC transplantation, two did not obtain a sufficient autograft to proceed to transplant and two were excluded because of progressive disease associated with deteriorating performance status. The median time from initial diagnosis of breast cancer to transplant was 16 months (range 2.3–134.4) and the median time from mobilization chemotherapy to transplant was 33 days (18–100 days). Of the 33 patients undergoing repetitive high-dose therapy and transplant, 84 cycles of high-dose treatment were delivered. For all 84 cycles, the median time to ANC ⬎0.5 × 109/l and 1.0 × 109/l was 10 days (range 7–26) and 10 days (range 8–28), respectively. The median time to platelets greater than 20 × 109/l, 50 × 109/l and 100 × 109/l was 13 days (range 9–28), 19 days (range 10– 40) and 25 days (range 10–152), respectively. The recoveries according to mobilization regimen are detailed in Table 2. Discussion We demonstrate that the mobilization regimens reported here have effective anti-tumor activity while mobilizing sufficient PBPCs in the majority of patients. Our prospective study demonstrates that 33 of the 37 (89%) patients obtained sufficient PBPCs while maintaining at least stable enough disease to undergo high-dose therapy with subsequent rapid platelet and neutrophil recovery. Although ifosfamide has previously been incorporated into chemotherapy regimens to mobilize PBPCs,8–14 these studies have not been restricted to patients with breast cancer,8–11,14 and those with breast cancer have generally been minimally pre-treated and not had metastatic or relapsed disease.12,13 The choice of the most appropriate mobilization regimen for patients with previously treated disease is further limited by prior cyclophosphamide and/or anthracycline exposure. Based on the findings reported here, we believe that the combination of ifosfamide with either doxorubicin or paclitaxel is an appropriate strategy in such patients. Nonetheless, 27% of patients who were refractory to prior conventional-dose therapy remained resistant to the ifosfamide-based regimen. The ifosfamide-paclitaxel and ifosfamide-doxorubicin regimens appeared at least equally efficacious in mobilizing PBPCs, with equivalent CD34+ cells mobilized into the PB, similar mobilization kinetics and equivalent yields in the PBPC collections. There was a trend toward better CD34+ cell collections in the ifosfamide-doxorubicin group (P = 0.059) and this appears to have translated into a trend toward slower neutrophil and platelet recovery following high-dose therapy (Table 2). However, the paclitaxel group was more heavily pre-treated with worse disease characteristics and may reflect the trend toward poorer mobilization. In this study the median time to initiate collection was day 10 after mobilization, however, this varied by 2 days either way. We have previously demonstrated the value of a morning PB CD34 count in predicting PBPC yield,31 and the results presented here demonstrate that by using an

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appropriate PB CD34+ cell trigger to initiate collection, the timing of harvesting can be optimized with approximately 3 × 106 CD34 cells/kg collected each day. Six patients required a second cycle of mobilisation and collection. The yield of these second collections was generally poor, particularly if the first collection had failed. Similar findings in myeloma patients undergoing second collection has previously been demonstrated.33 The overall response rate for all patients was 57% with an additional 19% of patients having stable disease. Three patients developed progressive disease during the mobilization phase. Furthermore, if only evaluable patients were analyzed (ie bi-dimensionally measurable disease), 68% of such patients responded. Indeed, our cohort had poor disease characteristics; patients had a median of two prior regimens, 15 having refractory disease, 81% had received prior cyclophosphamide, and 30% patients had received prior taxane therapy. These response rates are comparable to other studies utilizing ifosfamide in combination chemotherapy in MBC.16,20–23 Although there was a better response in the ifosfamide-doxorubicin group (75% vs 23%; P = 0.0046), the pre-treatment characteristics in the paclitaxel group were worse. One important aspect of this study was to determine if ifosfamide (6 g/m2) could be delivered safely as a 24 h infusion. A relatively short duration of infusion was required; the postulate being that a short exposure (as compared to the frequently used ifosfamide administration over 3–5 days in divided doses) would allow more synchronous, and possibly more efficacious, mobilization of PBPCs. Indeed, this regimen was associated with tolerable sideeffects. No red cell or platelet transfusions were required following mobilization and there were no episodes of febrile neutropenia. Given the pharmacokinetics of a 3 h paclitaxel infusion, it was not surprising that neutrophil and platelet nadirs following mobilization were lower in the ifosfamide-doxorubicin group. There were no episodes of hemorrhagic cystitis although one patient developed reversible neurotoxicity. We conclude that ifosfamide-based chemotherapy with G-CSF in combination with doxorubicin or paclitaxel achieves effective mobilization of PBPC and anti-tumor activity with acceptable toxicity.

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Acknowledgements

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We wish to thank Asta Medica (Sydney, Australia) and FH Faulding (Adelaide, Australia) for their generous support of this study, the research nurses, apheresis nurses and nursing staff on the Haematology and Day Wards at Peter MacCallum Cancer Institute for commitment, dedication and expert patient care.

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