Table 5

Joint effect of occupational formaldehyde and wood exposure on risk of NPCa

WoodFormaldehyde
None≤10 years>10 years
None1.0 (272/270)1.3 (23/16)1.7 (28/13)
≤10 years1.4 (12/8)1.0 (5/5)1.8 (4/2)
>10 years2.6 (17/6)(3/0)1.8 (11/5)
  • a Numbers presented are RR estimates adjusted for age, sex, education, ethnicity, and HLA. Numbers in parentheses correspond to the number of cases/controls. 95% CI for all individual RR estimates overlap 1. ptrend for wood in the absence of formaldehyde = 0.04 and for formaldehyde in the absence of wood = 0.09.