High Rate of Head-and-Neck Cancer in Women Pinned to Smoking

ROCKVILLE. Md., Aug. 27 -- Women appear to be particularly vulnerable to head-and-neck cancer from smoking, according to National Cancer Institute researchers.
Men are about three times likelier to develop squamous cancers of the head and neck than women, but smoking may be to blame for the larger relative increase in these cancers in women, Christian C. Abnet, Ph.D., of the National Cancer Institute here, and colleagues, reported online in the Oct. 1 issue of Cancer.
Head-and-neck cancer includes squamous tumors at multiple sites including the oral cavity, oropharynx, hypopharynx, and larynx.
Five-year survival in the U.S. varies by cancer subsite, from 31% in the hypopharynx to 64% in the larynx, with cigarette smoking thought to be the strongest risk factor for the larynx, the researchers wrote.
The researchers' findings emerged from a study of 476,211 participants, ages 50 to 71, in the National Institutes of Health/American Association of Retired Persons (NIH-AARP) diet and health study.
At baseline, the median age of the cohort was 62.6. About 60% were men, well educated (20.4% had completed graduate school), and non-Hispanic white (92.6%).
Only 36.5% were never-smokers, and the rest were former or current smokers. Although more women than men were never smokers, and more men were former smokers, more women were current smokers than men, the researchers found.
Over the course of follow-up (1995 through 2000), 584 men and 175 women were diagnosed with head-and-neck cancer.
Among men, nonsmokers (24.4%), former smokers (36.9%), and current smoking (147.3) had higher rates of age-adjusted incidence of head and neck cancer per 100,000 person-years of follow-up than women did in each equivalent category of cigarette use.
For example, the researchers wrote, the age-adjusted incidence per 100,000 person years was 147.3 for men versus 75.7 for women.
However, the hazard ratios for head and neck cancer overall associated with smoking were significantly larger in women (12.96; 95% confidence interval [CI], 7.81-21.52) than in men (5.45, CI, 4.22-7.05; P for interaction <0.001).
This was also true for the three subsites (oral cavity, oro-hypopharynx, and larynx) examined in stratified analyses.
Thus ever-smoking accounted for 45% of head and neck cancers in men and 75% in women, assuming causality, the researchers said.
The larger hazard ratios in women relative to men could be the result of women having higher rates of cancer at the same exposure level or differences in rates in the nonsmoking referent groups, they speculated.
Other potential explanations for some of the differences were the possibility that the diagnosis of head-and-neck cancer was missed more often in women than in men in this study, although this is unlikely because men and women are generally diagnosed at similar stages.
It is also unlikely, they said, that diagnoses in this study were dependent on smoking status. Alternatively men and women may have varied in the accuracy of their responses to the smoking questions.
The researchers said that compared with women more men with head and neck cancers were never-smokers, suggesting that they are exposed to other risk factors, although alcohol use and pipe and cigar smoking were ruled out.
Occupational, hormonal (steroid hormones, for example), or viral factors (human papilloma virus) could have been involved, especially exposure to second-hand tobacco smoke.
Study limitations noted were lack of information on smoking duration, occupation, and smokeless tobacco use.
Finally, they said, this cohort was more educated, and less likely to include current smokers than the general U.S. population, perhaps limiting the generalizability to other subpopulations.
"Although we believe that the mechanism underlying these differences in the baseline risk observed in men and women merits further investigation, our results suggest that smoking is a strong risk factor for head and neck cancer in both sexes, and public health interventions should continue to focus on reducing smoking use by all," Dr. Abnet and his colleagues concluded.
No financial conflicts were reported. This study was supported by the Intramural Research Program of the National Institutes of Heath, National Cancer Institute. Primary source: CancerSource reference: Freedman ND, et al "Prospective Investigation of the Cigarette Smoking-Head and Neck Cancer Association by Sex" Cancer 2007; doi: 10.1002/cncr.22957.