INTRODUCTION
Sarcomas represent a heterogeneous group of rare tumors with a variety
of histological and biological characteristics and different prognosis.
In pediatric age, rhabdomyosarcoma (RMS) is the most common histotype.
Like Ewing sarcoma (ES) and desmoplastic small round cell tumors
(DSRCT), RMS is a high-grade tumor with a strong tendency for local
invasiveness and metastatic spread. These tumors are currently treated
using a multidisciplinary approach that includes surgery, radiotherapy,
and intensive multi-agent chemotherapy. While the outcome of treatment
for patients with localized RMS and ES is generally a 70-80% survival
rate, the outcome remains unsatisfactory for patients with distant
metastases and those who relapse (1) (2). Patients with DSRCT still
carry a poor prognosis in most cases (3) and, together with those who
have metastatic or relapsed RMS and ES, form a high-risk group for whom
new treatment approaches need to be investigated.
The use of new drugs to target specific molecular alterations is an
attractive approach for poor prognosis sarcomas. However, at this time,
the activity data of these new agents is still limited (4) (5). An
improvement in the outcome of children with high-risk sarcomas may also
be pursued by optimizing the use of already-available drugs known to be
active against this disease. The treatment of pediatric sarcomas is
currently based on administering chemotherapy cycles containing multiple
drugs every three weeks. It may be that cancer cells start growing again
during the interval between chemotherapy cycles and develop a resistance
to the drugs administered.
Reducing the time between chemotherapy cycles to intensify the treatment
has proved feasible and effective in the treatment of ES (6) and, to
some degree, for metastatic RMS (7). Higher treatment intensity can also
be achieved by increasing the dosage of drugs per unit of time,
according to the so-called dose-density approach.
Irinotecan is active against various pediatric tumors, including RMS and
other sarcomas (8). As it is relatively non-myelotoxic, we hypothesized
that it might be associated with other more myelotoxic drugs.
In this study, we explored the feasibility of a dose-density strategy
for patients with high-risk soft-tissue sarcomas that involved a novel
combination of irinotecan with a more standard regimen based on
alkylating agents. This represents a proof of concept that will be
further investigated in the next multicenter trial coordinated by the
European pediatric Soft tissue sarcoma Study Group (EpSSG).
METHOD
This study included patients with a histologically confirmed diagnosis
of RMS, ES, or DSRCT with metastasis at diagnosis or with
relapsed/refractory disease. To be eligible, patients had to be
>6 months and ≤ 21 years old, and have: a Karnofsky
performance status of 70-100% (for patients >12 years old)
or a Lansky Play Score of 70-100% (for patients ≤12 years of age); an
adequate bone marrow function (absolute neutrophil count
≥1000/mm3, platelet count
≥100,000/mm3); adequate renal and liver function; and
no active grade >2 diarrhea or uncontrolled infection.
The study was approved by the local ethical committee, and informed
consent was obtained from patients or parents, as appropriate.
The diagnostic workup consisted of CT and/or MRI scans of the primary
tumor, chest CT scan, radionuclide bone scan, bone marrow aspirate, and
biopsy. 18F-fluorodeoxyglucose PET was optional.
TREATMENT
As detailed in Figure 1, the first part of the regimen investigated
consisted of IVA ( ifosfamide at a dose of 3g/m2 on
Days 1 and 2 as a 3-hour intravenous infusion (iv) (with sodium
mercaptoethanesulfonate at a dose of 3 g/m2 per day
and hyperhydration); vincristine at a dose of 1.5
mg/m2 ( maximum, 2 mg) on Day 1 given as a single
bolus dose by intravenous injection; actinomycin at a dose of 1.5
mg/m2 (maximum, 2mg) on Day 1 given as a single bolus
by
intravenous injection, VAC (vincristine 1.5 mg/m2 iv,
actinomycin D 1.5 mg/m2 iv, and cyclophosphamide 1.5
mg/m2, all on day 1) currently used respectively by
the EpSSG in Europe, and by the Children’s Oncology Group (COG) in the
USA. VAC was administered to patients that received ifosfamide in the
first line. Irinotecan was started on day 8 and given for 5 days
(preferably Monday to Friday to enable its administration in the
outpatient setting), irrespective of blood cell counts, providing the
patient was in good clinical conditions. Since this was the first
attempt to include irinotecan in a dose-density multidrug combination, a
fixed, reduced dose of irinotecan was used (20
mg/m2/day for 5 consecutive days) to gather
information and ascertain whether a subsequent formal phase I trial
would be possible. Diarrhea prophylaxis included the administration of
cefixime 8 mg/kg per os once a day for 9 consecutive days starting on
day 6.
Cycles were administered every 21 days, with neutrophils
>1.0 x 109/l and platelets to
>100 x 109/l and following resolution of
non-hematopoietic toxicity. The preventive use of colony-stimulating
factors was not allowed. Tumor response was scheduled to be assessed
after 3 and 9 cycles at the site of both the primary tumor and any
metastases, and more assessments were possible if clinically indicated.
The response was classified as: complete response (CR) = complete
disappearance of all visible disease; partial response (PR) = a tumor
volume reduction of more than two-thirds; minor response (MR) = a tumor
volume reduction of more than one-third, but less than two-thirds. A
reduction in volume of less than one-third was recorded as stable
disease (SD), while an increase in tumor size or the detection of new
lesions was classified as progression of disease (PD)
Local treatment with radiotherapy and/or surgery had to be considered
after the 4th cycle of chemotherapy, but only general
recommendations were given because of the heterogeneity of the study
population. Resection was recommended for primary tumors with/without
metastases, if feasible. Radiotherapy also had to be considered for
primary and metastatic sites in newly-diagnosed metastatic sarcomas. If
possible, re-irradiation was recommended in relapsed patients.