83
The rest of this chapter is organized as follows. Section 4.2 describes the mo-
tivating phase II sarcoma dataset. The non-exchangeable model is formalized and
discussed in detail in Section 4.3. Section 4.4 reports a comparison of the proposed
model versus several alternatives. In Section 4.5 the model is applied to the sarcoma
data. Section 4.6 concludes with a discussion.
4.2 Data
A single arm Phase II clinical trial for sarcoma is carried out at M.D. Anderson Cancer
Center. The objective of the study is to asses the efficacy of Irinotecan on patients
with different sarcoma subtypes. Irinotecan is a water soluble and commercially
available chemical agent that is thought to reduce the sarcoma cancerigenic tumors.
Its Dose-Limiting Toxicity (DLT) has been measured through a Phase I clinical trial
(Masuda et al, 2000). The DLT is defined as diarrhea and bone marrow suppression.
The patients in this trial received the drug in cycles of 21 days, where the drug was
administered during the first two weeks and nothing during the third one. A week
with drug treatment consisted of 16 mg∕m2 of daily injections of Irinotecan for five
consecutive days and two days of resting.
Treatment efficacy is measured as tumor shrinkage. More specifically, tumor sizes
at the end of the second cycle and, if necessary, at the end of the fourth cycle were
compared with the size at the beginning of the study. If complete (total disappearance
of tumor) or partial responses (at least 30% shrinkage) is observed at the end of the
second cycle, the treatment is considered a success for this patient. In contrast, when
reporting progressive disease (20% or more increase), the trial is declared a failure.
If none of the above criteria is met, the disease is considered stabilized. In this case,
the tumor is measured again after the fourth cycle, and the treatment is declared a
failure only when progressive disease is reported.
This study is still ongoing. So far, a total of 179 patients have met the eligibility
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