Table 2. Multivariate Analysis of PFS and OS on the Basis of p16, Cetuximab, and KRAS-Variant Status.
| Variable | PFS (n = 116 Events) |
OS (n = 85 Events) |
||
|---|---|---|---|---|
| HR (95% CI)a | P Value | HR (95% CI)a | P Value | |
| Treatment × KRAS | ||||
| × p16 | NA | .20 | NA | .02 |
| If p16-positive | NA | .14 | NA | .05 |
| Treatment × p16 | ||||
| If KRAS-variant | NA | .51 | NA | .15 |
| If KRAS-nonvariant | NA | .12 | NA | .01 |
| KRAS × p16 | ||||
| If cetuximab | NA | .84 | NA | .11 |
| If no cetuximab | NA | .04 | NA | .10 |
| Treatment effect | ||||
| If KRAS-variant and p16 positive | 0.60 (0.17-2.10) | .42 | 0.21 (0.02-2.04) | .18 |
| If KRAS nonvariant and p16 positive | 1.74 (0.88-3.42) | .11 | 2.36 (0.98-5.67) | .05 |
| KRAS effect | ||||
| If no cetuximab and p16 positive | 2.59 (0.91-7.33) | .07 | 2.48 (0.64-9.65) | .19 |
| If cetuximab and p16 positive | 0.89 (0.34-2.35) | .82 | 0.22 (0.03-1.66) | .14 |
| p16 effect | ||||
| If cetuximab and KRAS-variant | 0.73 (0.20-2.73) | .64 | 0.12 (0.01-1.11) | .06 |
| If cetuximab and KRAS nonvariant | 0.63 (0.36-1.11) | .11 | 0.80 (0.41-1.54) | .50 |
| If no cetuximab and KRAS-variant | 1.34 (0.40-4.44) | .64 | 0.86 (0.20-3.64) | .84 |
| If no cetuximab and KRAS nonvariant | 0.32 (0.17-0.61) | <.001 | 0.21 (0.09-0.49) | <.001 |
Abbreviations: HR, hazard ratio; NA, not applicable (HRs for interaction terms are not meaningful and are therefore note reported); OS, overall survival; PFS, progression-free survival.
a
The HRs were estimated from Cox proportional hazards models, including treatment (cetuximab vs no cetuximab), treatment × PFS and OS time interaction, KRAS (variant vs nonvariant), treatment × KRAS interaction, treatment × PFS and OS time × KRAS interaction, age, Zubrod performance status (1 vs 0), primary site (oropharynx vs others), T stage (T4 vs T2-3), and N stage (N2b-3 vs N0-2a).