  Purpose: PFS is often used as a surrogate endpoint for OS in metastatic
breast cancer studies. We have evaluated the association of treatment effect on
PFS with significant HR$_{OS}$ (and how this association is affected by other
factors) in published prospective metastatic breast cancer studies.
  Methods: A systematic literature search in PubMed identified prospective
metastatic breast cancer studies. Treatments effects on PFS were determined
using hazard ratio (HR$_{PFS}$), increase in median PFS ($\Delta$MED$_{PFS}$)
and % increase in median PFS (%$\Delta$MED$_{PFS}$). Diagnostic accuracy of PFS
measures (HR$_{PFS}$, $\Delta$MED$_{PFS}$ and %$\Delta$MED$_{PFS}$) in
predicting significant HR$_{OS}$ was assessed using receiver operating
characteristics (ROC) curves and classification trees approach.
  Results: Seventy-three cases (i.e., treatment to control comparisons) from 64
individual publications were identified for the analyses. Of these, 16 cases
reported significant treatment effect on HR$_{OS}$ at 5% level of significance.
Median number of deaths reported in these cases were 156. Area under the ROC
curve (AUC) for diagnostic measures as HR$_{PFS}$, $\Delta$MED$_{PFS}$ and
%$\Delta$MED$_{PFS}$ were 0.69, 0.70 and 0.75, respectively. Classification
tree results identified %$\Delta$MED$_{PFS}$ and number of deaths as diagnostic
measure for significant HR$_{OS}$. Only 7.9\% (3/39) cases with
$\Delta$MED$_{PFS}$ shorter than 48.27\% reported significant HR$_{OS}$. There
were 7 cases with $\Delta$MED$_{PFS}$ of 48.27\% or more and number of deaths
reported as 227 or more -- of these 5 cases reported significant HR$_{OS}$.
  Conclusion: %$\Delta$MED$_{PFS}$ was found as better diagnostic measure for
significant HR$_{OS}$. Our analysis results also suggest that consideration of
total number of deaths may further improve its diagnostic performance.
