Table 3.

Incidence and adjusted hazard ratio (95% CI) of developing nasopharyngeal carcinoma by cigarette smoking habit

VariableParticipant number (%)Person-yearsNasopharyngeal carcinoma
Case no.Incidence rate*Hazard ratio (95% CI)
Cigarette smoking
    Never3,316 (34.6)61,461.9914.61.0 (reference)
    Ever6,279 (65.4)111,737.62320.61.2 (0.6-2.6)
    Missing27506.200
Quantity of cigarette smoking (pack/d)
    Never3,316 (35.1)61,461.9914.61.0 (reference)
    <12,641 (28.0)46,703.4612.8
    ≥13,491 (36.9)62,473.61727.21.7 (0.9-3.5)
    Missing1743,066.700
Duration of cigarette smoking (y)
    Never3,316 (35.6)61,461.9914.61.0 (reference)
    <303,008 (32.3)59,944.4711.7
    ≥302,990 (32.1)47,072.81429.73.2 (1.2-8.8)
    Missing3085,226.6238.3
Cumulative exposure to cigarette smoking (pack-years)
    Never3,316 (35.8)61,461.9914.61.0 (reference)
    <303,883 (41.9)72,923.6912.3
    ≥302,074 (22.3)33,382.11235.93.0 (1.3-7.2)
    Missing3495,938.0233.7
  • * Per 100,000 person-years.

  • Adjustment for age, anti–EBV viral capsid antigen immunoglobulin A, and anti–EBV DNase.

  • P < 0.05.