BACKGROUND: Standard, nonparametric statistical methods measure the interaction of covariates with survival rate or relative risk. Conversely, parametric methods measure the interaction of covariates with the two cardinal features of malignant potential: the likelihood of cure and the median time to relapse among uncured patients. METHODS: The authors performed parametric analysis on data from 810 patients with breast cancer using relapse as the survival end point. Prognostic covariates included lymph node status, tumor size, patient age, nuclear size, S-phase by thymidine or bromodeoxy-uridine labeling, and type of adjuvant therapy (chemotherapy, radiation, or hormone therapy). Also included was the cross-product term (labeling index X chemotherapy). RESULTS: Multivariate analysis revealed that: likelihood of cure was associated positively with labeling index X chemotherapy and associated negatively with lymph node status, tumor size, and patient age; and time to relapse was associated negatively with node status, nuclear size, and labeling index. CONCLUSION: The associations of labeling index and chemotherapy with the clinical course suggest that rapidly dividing tumors have a high likelihood of cure, especially with adjuvant chemotherapy, but those not cured may have early relapse.
BACKGROUND: Standard, nonparametric statistical methods measure the interaction of covariates with survival rate or relative risk. Conversely, parametric methods measure the interaction of covariates with the two cardinal features of malignant potential: the likelihood of cure and the median time to relapse among uncured patients. METHODS: The authors performed parametric analysis on data from 810 patients with breast cancer using relapse as the survival end point. Prognostic covariates included lymph node status, tumor size, patient age, nuclear size, S-phase by thymidine or bromodeoxy-uridine labeling, and type of adjuvant therapy (chemotherapy, radiation, or hormone therapy). Also included was the cross-product term (labeling index X chemotherapy). RESULTS: Multivariate analysis revealed that: likelihood of cure was associated positively with labeling index X chemotherapy and associated negatively with lymph node status, tumor size, and patient age; and time to relapse was associated negatively with node status, nuclear size, and labeling index. CONCLUSION: The associations of labeling index and chemotherapy with the clinical course suggest that rapidly dividing tumors have a high likelihood of cure, especially with adjuvant chemotherapy, but those not cured may have early relapse.