Increased ornithine decarboxylase (ODC) activity, measured biochemically in breast cancers, has been associated with increased risk for recurrence of disease and death. Recently an immunohistochemical (IHC) method for ODC determinations in formalin-fixed paraffin-embedded tissues has been developed. We used this IHC ODC assay to evaluate primary breast cancers from 433 Vietnamese premenopausal women participating in a clinical trial of adjuvant combined hormonal therapy. Using an H SCORE system (intensity of staining 0-3 x percentage of all cells; possible range 0-300), 52% of tumors had an ODC score of < or = 35; 12% had a score of > or = 100. No statistically significant correlations of ODC H SCORES and usual prognostic factors were found; a negative weak correlation with weight was demonstrated (Spearman -0.12; p = 0.01). Using two cutoff scores, high and low ODC groups were similar in prognostic factors, except for high histologic grade which was more common with higher ODC H SCORES. Univariate, Kaplan-Meier and multivariate Cox analyses showed no evidence of relationships of ODC by H SCORE to disease-free or overall survival.