A population-based case control study of papillary thyroid cancer involved 558 women aged 18-64 with thyroid cancer diagnosed between 1988-1994, 468 (84%) were interviewed. Analyses were confined to women with papillary histology (n=410). Controls (n=574) were selected by random digit dialling (response rate 73.6%) Logistic regression analysis was used to calculate odds ratios and corresponding confidence intervals estimating the relative risk of papillary thyroid cancer associated with smoking and drinking. If at the time of cancer diagnosis women used alcohol or smoked they were considered current smokers or drinkers, for controls at a comparable reference data.

A history of ever having smoked more than 100 cigarettes was associated with a reduced risk (OR 0.7, 95% CI 0.5-0.9) with the risk reduction being most pronounced in current smokers (OR 0.5, 95% CI 0.4-0.7. Women who reported they had consumed 12 or more alcoholic drinks within a year also had a lowered risk (OR 0.7, 95% CI 0.5-1.0). As for smoking the risk reduction was most prominent for current drinkers. The risk reduction was greater for women aged >45 years (OR 0.4, 95% CI 0.2-0.7) than for younger women (OR 0.8, 95% CI 0.6-1.2).

The results suggest that the effects of alcohol and tobacco on thyroid cancer risk are of relatively short duration, but the association found, if not attributable to chance, may be related to the effects of smoking and drinking on reducing thyroid cell proliferation through effects on TSH, oestrogen or other mechanisms.

Source. Rossing MA, Cushing KL, Voigt LF, Wicklund KG. Risk of papillary thyroid cancer in women in relation to smoking and alcohol consumption. Epidemiology 11 (2000) 49-54.