Patients undergo blood collection for pharmacokinetic sampling of dactinomycin at baseline (prior to the initiation of dactinomycin) and periodically during course 1 of chemotherapy. An additional blood sample is obtained before or after treatment for the collection of peripheral blood lymphocytes. DNA from these cells is isolated and investigated for genetic variation in genes relevant to the pharmacology of dactinomycin. Plasma concentrations of dactinomycin are determined by liquid chromatography mass spectrometry analysis.