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Experts Consider Statistical Issues in Designing Studies of Toxicity Modifiers

Experts Consider Statistical Issues in Designing Studies of Toxicity Modifiers

PHILADELPHIA—In designing trials of potential toxicity modifiers,
consideration must be given to endpoint selection and correlation of
endpoints, as well as sample size and analysis methods. Important design
factors were reviewed by Charles B. Scott, PhD, associate director of
quality of life research at the American College of Radiology in
Philadelphia.

"For our toxicity endpoint, we need to be concerned about the timing
of data collection," Dr. Scott said. "How often do you have the
patient come back to the clinic to collect data in order to be able to
compute the time of resolution? When does the toxicity occur?"

Quality of life endpoints should be assessed prior to initiation of
therapy, at the peak of toxicity, and periodically in follow-up to correlate
with toxicity resolution, he noted.

"The clinical endpoints we want to collect in any toxicity modifier
trial are survival and tumor response, just to make sure that we don’t
have an adverse effect on those clinical endpoints," Dr. Scott said.

Meaningful Differences

Consideration of the clinically meaningful difference is also important.
As an example, Dr. Scott used the development of amifostine (Ethyol). This
development, he said, "was built more around the maximum tolerated dose
rather than that dose which leads to clinical efficacy. What is that
meaningful difference? Do we look at a 25% reduction in grade 3 to 4
esophagitis? Or do we look at a 50% reduction in rectal bleeding? What is
the point at which we say that it makes a true effect on the patient? How
much do we have to reduce it? We can look at any type of difference
statistically, but what is the level at which it’s truly meaningful?"
Dr. Scott said.

Researchers expect to see correlations between interventions and
endpoints. Dr. Scott said that symptom-specific quality of life may
correlate with toxicity. A number of scales can be used to assess these
factors, such as the Functional Assessment of Cancer Therapy, the Head and
Neck Performance Status Scale, and the University of Washington Quality of
Life Scale.

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