Background: Interactions between prognostic and pharmacodynamic (PD) biomarkers have received little attention.
Methods: Prognostic and PD utilities were assessed with linear mixed-effects models using published data on repeated measurements of circulating caspase-cleaved (ctCK18) and total (tCK18) cytokeratin 18, in 57 patients with metastatic colorectal cancer undergoing chemotherapy.
Results: The model for tCK18 (but not cCK18) separated the prognostic/PD interaction from the pure prognostic effect, illustrating the principle of dual prognostic and PD characteristics for a given biomarker.
Conclusion: These models provide the framework for the analysis and interpretation of longitudinal data to detect prognostic/PD biomarker interactions.