Table 3.
Univariate and multivariate analyses for disease-free survival.
| Variable | Univariate | Multivariate | ||||
|---|---|---|---|---|---|---|
| Stepwise Selection * | Selected Predictors # | |||||
| HR | 95% CI | HR | 95% CI | HR | 95% CI | |
| Covariate | ||||||
| p16 (ref. = negative) | 0.31 | (0.17, 0.56) | 0.12 | (0.03–0.58) | 0.10 | (0.02, 0.49) |
| Gender (ref. = male) | 0.32 | (0.12, 0.88) | 1.12 | (0.36, 3.42) | ||
| Age (5-year increments) | 0.98 | (0.87, 1.11) | 1.12 | (0.97–1.28) | ||
| Clinical stage (ref. = stage I–III) & | ||||||
| Stage IVA | 2.75 | (1.09, 6.90) | 3.6 | (1.37–9.45) | 2.87 | (1.11, 7.41) |
| Stage IVB | 10.68 | (3.88, 29.41) | 12.35 | (4.09–37.26) | 8.43 | (2.83, 25.08) |
| Tumor subsite (ref. = other sites than tonsil) | 0.34 | (0.21, 0.55) | 0.49 | (0.26–0.83) | 0.46 | (0.27, 0.80) |
| Initial treatment (ref. = surgery) | 1.05 | (0.62, 1.78) | 1.21 | (0.68, 2.16) | ||
| Smoking age (ref. = <20 pack-years) | ||||||
| 20–29 | 1.43 | (0.71, 2.88) | 1.69 | (0.77–3.70) | 1.64 | (0.74, 3.63) |
| ≥30 | 2.07 | (1.20, 3.55) | 1.88 | (1.01–3.49) | 1.99 | (1.06, 3.75) |
| Alcohol use (ref. = none) | 2.68 | (1.37, 5.23) | 0.66 | (0.27–1.62) | 0.57 | (0.23, 1.39) |
| Betel quid chewing (ref. = none) | 1.77 | (1.08, 2.92) | 0.91 | (0.48, 1.72) | ||
| Interaction term | ||||||
| p16: Smoking age (20–29 pack-years) | ||||||
| p16: Smoking age (≥30 pack-years) | ||||||
| p16: Alcohol use | 4.4 | (0.78–24.7) | 6.00 | (1.03, 35.01) | ||
| 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.