Table 2.
Univariate and multivariate analyses for overall survival.
| Variable | Univariate | Multivariate | ||||
|---|---|---|---|---|---|---|
| Stepwise Selection * | Selected Predictors # | |||||
| HR | 95% CI | HR | 95% CI | HR | 95% CI | |
| Covariate | ||||||
| p16 (ref. = negative) | 0.18 | (0.09, 0.37) | 0.08 | (0.02, 0.35) | 0.09 | (0.02, 0.44) |
| Gender (ref. = male) | 0.15 | (0.04, 0.60) | 0.52 | (0.12, 2.33) | ||
| Age (5-year increments) | 0.89 | (0.78, 1.02) | ||||
| Clinical stage (ref. = stage I–III) & | ||||||
| Stage IVA | 2.69 | (1.07, 6.76) | 2.55 | (1.00, 6.49) | 2.72 | (1.05, 7.00) |
| Stage IVB | 12.11 | (4.41, 33.26) | 16.26 | (5.76, 45.86) | 15.62 | (5.29, 46.13) |
| Tumor subsite (ref. = other sites than tonsil) | 0.46 | (0.28, 0.73) | 0.77 | (0.45, 1.33) | ||
| Initial treatment (ref. = surgery) | 0.88 | (0.52, 1.48) | 1.02 | (0.58, 1.81) | ||
| Smoking age (ref. = <20 pack-years) | ||||||
| 20–29 | 1.78 | (0.85, 3.70) | 0.96 | (0.41, 2.23) | 1.15 | (0.46, 2.90) |
| ≥30 | 2.98 | (1.67, 5.32) | 1.90 | (1.02, 3.54) | 2.05 | (1.05, 4.00) |
| Alcohol use (ref. = none) | 3.19 | (1.58, 6.44) | 0.90 | (0.39, 2.08) | ||
| Betel quid chewing (ref. = none) | 2.35 | (1.40, 3.96) | 0.85 | (0.45, 1.61) | ||
| Interaction term | ||||||
| p16: Smoking age (20–29 pack-years) | 8.00 | (1.16, 55.01) | 5.74 | (0.79, 41.53) | ||
| p16: Smoking age (≥30 pack-years) | 2.94 | (0.43, 19.93) | 2.53 | (0.36, 17.85) | ||
| p16: Alcohol use | ||||||
| p16: Betel quid chewing | ||||||
* Variable selection employed the stepwise method by the Akaike information criterion. # The Cox proportional hazard model was constructed with interaction terms that were selected by the stepwise method and significant and clinically relevant variables from univariate analyses. & The clinical stage was defined by the 7th edition of the American Joint Committee on Cancer (AJCC) staging system. Significant values of HR and 95% CI are in bold. Abbreviations: HR, hazard ratio; CI, confidence interval; ref., reference.