Outcome
After the initial three cycles, CR was evident in 3 patients, PR in 15,
and MR in 1. SD was evident in the 2 children with RMS and PD in 2
patients with Ewing sarcoma. Considering the CR and PR alone, the
response rate was 88.2% (15/17) in cases of RMS. PR was evident in 2/4
patients with relapsed ES and 1/2 patients with DSRCT. The response
rates were 84.6% (11/13) and 70% (7/10) for patients treated with
IrIVA and IrVAC, respectively.
With a median follow-up of 2.6 years (range 0.2 -5.0), 12 patients were
still alive at the time of writing, 9 in CR (3 metastatic at diagnosis
and 6 with the relapsing disease) and 3 were alive with disease.
DISCUSSION
In this study, we evaluated the feasibility of a dose density approach
using a chemotherapy combination that aimed to include irinotecan in the
chemotherapy regimens currently used to treat patients with sarcoma, and
especially RMS.
The IVA regimen is now considered the standard chemotherapy in European
trials for non-metastatic RMS. In North America, cyclophosphamide is
used instead of ifosfamide in the VAC regimen. The most significant
toxicity of these two combinations is myelotoxicity in the 2-3 weeks
following their administration. Irinotecan is a drug active against RMS
and, when administered with a continuous schedule (i.e., over 5 days for
1 week), its worst side effect is diarrhea, while myelotoxicity is low.
The IrIVA or IrVAC regimens are, therefore, rational combinations of the
standard IVA/VAC scheme with irinotecan because the activity of the
drugs and their different toxicity profiles theoretically allow an
increase of the chemotherapy intensity without increasing the risk of
toxicity.
This was confirmed in our study. Most of the patients were able to
complete their treatment within a reasonable time. Although IrIVA/IrVAC
are intensive combinations, toxicity was not significantly worse than in
patients treated with IVA in the RMS2005 protocol, where grade 3-4
infections were reported in 57% of patients, and renal and
gastrointestinal toxicity in 2% and 8%, respectively (10). It should
be noted that 47.8% of the patients in our present study had a relapsed
tumor, so they had already received previous treatments, meaning that a
more significant toxicity might have been expected.
There is limited experience of the dose-density approach against
pediatric sarcoma. An attempt to reduce the interval between cycles
proved feasible, and possibly beneficial, in patients with metastatic
RMS included in the COG protocol ARST0431study was based on the concept
of dose-compression: the cycles of chemotherapy were administered with
an interval of 14 days instead of the 21 as it is used in the standard
treatment. The results showed a possible improvement for patients with
embryonal RMS, but not for those with high-risk features (Oberlin score
>1) (7). More promising results were achieved in localized
ES by adopting the same chemotherapy-intensifying approach and reducing
the interval between cycles to 2 weeks. A randomized study reported a
significantly better outcome in patients treated with chemotherapy
administered after shorter intervals than in those given the same
chemotherapy according to the standard interval (6). New combinations
are under study using the same approach (11).
In our high-risk population, 52% of patients were alive in CR at the
time of writing, although some have only a short follow-up. This result,
and the limited toxicity reported, indicate that the IrIVA or IrVAC
combinations deserve further testing, possibly in a more homogenous
group of patients with less unfavorable features-as already done for ES
patients (6) (11).
A limitation of our study is that we tested only one dose of irinotecan
(20 mg/m2/day for 5 days). The recommended dose of
irinotecan, when it is used alone or with vincristine, is 50
mg/m2 for 5 days. Therefore a proper phase I study is
needed to establish the maximum tolerated dose of irinotecan within this
novel regime.
In conclusion, our study demonstrates that it is feasible to include
irinotecan in the standard chemotherapy regimens used to treat sarcoma,
and its use in this setting deserves further investigation. This will be
one of the goals of the next EpSSG study.