The Value of Early Depth of Response in Predicting Long-Term Outcome in EGFR-Mutant Lung Cancer.

INTRODUCTION

Traditionally, marked tumor shrinkage has been assumed to portend better outcome. We investigated whether depth of tumor response was associated with improved survival outcomes in advanced EGFR-mutant NCLC.

METHODS

Individual patient data from randomized trials (EURTAC, IPASS, ENSURE, LUX-Lung 3, and LUX-Lung 6) were used. The association of depth of response with progression-free survival (PFS) and overall survival was examined using landmark analyses. Depth of response based on radiologic assessments at 6 weeks and 12 weeks was calculated as the relative changes in the sum of the longest diameters of the target lesions from baseline.

RESULTS

Of 1081 evaluable patients at 6 weeks with no disease progression, 71.2% achieved Response Evaluation Criteria in Solid Tumors response. Using a landmark analysis, EGFR-TKI was more effective than chemotherapy (PFS hazard ratio = 0.36, p < .0001); and was associated with greater mean tumor shrinkage than chemotherapy (35.1% versus 18.5%, p < .0001). However, there was no significant difference in the relative PFS benefit between treatment groups across the entire spectrum of tumor shrinkage (p = .18 for test of interaction between treatment and continuously measured depth of response). Depth of response at 6 weeks was not associated with PFS when adjusted for treatment effect (hazard ratio = 0.96, p = .78). Similar results were obtained for 12-week landmark analysis and for OS outcome.

CONCLUSIONS

The PFS advantage of EGFR-TKI over chemotherapy in advanced EGFR mutant NCLC is not explained by depth of response at 6 or 12 weeks. It should not be used as a surrogate of benefit in future trials or routine clinical decision making.