PARAMETRIC SURVIVAL ANALYSIS OF ADJUVANT THERAPY FOR STAGE-II BREAST-CANCER

Background. Standard, nonparametric statistical methods estimate only the impact of therapy on survival rate up to a selected follow-up inte rval. In contrast, parametric methods can estimate the impact of treat ment on the two cardinal parameters of malignancy: likelihood of cure and recurrence free survival time among uncured patients. Methods. The authors screened a total of six parametric survival models. Three of these, including the log normal model, were applied to survival data f rom five clinical trials of adjuvant therapy for Stage II breast cance r. For comparison, the log rank test, a standard nonparametric method, was also applied to the same data. Results. Both parametric and nonpa rametric methods identified a significant therapeutic effect in three of the five trials. In only one of these three trials, however, did pa rametric analysis identify a significant difference in the likelihood of cure between treatment groups. In the remaining two trials, a signi ficant difference was found in recurrence free survival time among unc ured patients. The three parametric survival models gave similar resul ts. Conclusion. These findings suggest that parametric analysis may wa rrant further study as a method for measuring the long term clinical i mpact of adjuvant therapy on Stage II breast cancer.