Table 4.

Combined and stratified analysis of nasopharyngeal carcinoma risk by seromarkers of antibodies against EBV with cigarette smoking habit

Cigarette smokingCombination of VCA IgA/DNaseParticipant number (%)Person-yearsNasopharyngeal carcinoma
Case no.Incidence rate*Combined effect hazard ratio (95% CI)Stratum-specific effects hazard ratio (95% CI)
Quantity (pack/d)
    <1Both negative5,212 (55.5)95,442.21313.61.0 (reference)1.0 (reference)
    <1Any positive708 (7.5)12,005.3216.71.2 (0.3-5.4)1.3 (0.3-5.8)
    ≥1Both negative2,999 (31.9)53,844.8814.91.1 (0.5-2.6)1.0 (reference)
    ≥1Any positive476 (5.1)8,344.9825.97.0 (2.9-17.0)6.2 (2.3-16.7)
Test for interaction: P = 0.068
Duration (y)
    <30Both negative5,581 (60.3)107,551.71312.11.0 (reference)1.0 (reference)
    <30Any positive704 (7.6)13,086.1322.91.9 (0.6-6.8)1.9 (0.6-6.8)
    ≥30Both negative2,516 (27.1)39,920.1717.52.5 (0.8-7.8)1.0 (reference)
    ≥30Any positive461 (27.1)6,941.8686.412.5 (3.8-41.3)5.0 (1.7-14.9)
Test for interaction: P = 0.263
Cumulative exposure (pack-years)
    <30Both negative6,315 (68.5)118,635.21411.81.0 (reference)1.0 (reference)
    <30Any positive840 (9.1)14,939.4426.82.3 (0.8-7.1)2.3 (0.8-7.1)
    ≥30Both negative1,748 (19.0)28,248.3621.22.4 (0.8-6.7)1.0 (reference)
    ≥30Any positive317 (3.4)4,965.35100.711.4 (3.7-35.1)4.8 (1.5-15.9)
Test for interaction: P = 0.381
  • * Per 100,000 person-years.

  • Adjustment for age.

  • P < 0.01.