Smokeless tobacco and increased risk of hypopharyngeal and laryngeal cancers: a multicentric case-control study from India.

Hypopharyngeal and laryngeal cancers are among the most common cancers in India. In addition to smoking, tobacco chewing may be a major risk factor for some of these cancers in India. Using data from a multicentric case-control study conducted in India that included 513 hypopharyngeal cancer cases, 511 laryngeal cancer cases and 718 controls, we investigated smoking and chewing tobacco products as risk factors for these cancers. Bidi smoking was a stronger risk factor compared to cigarette smoking for cancer of the hypopharynx (OR(bidi) 6.80 vs. OR(cig) 3.82) and supraglottis (OR(bidi) 7.53 vs. OR(cig) 2.14), while the effect of the 2 products was similar for cancer of the glottis (OR(bidi) 5.32 vs. OR(cig) 5.74). Among never-smokers, tobacco chewing was a risk factor for hypopharyngeal cancer, but not for laryngeal cancer. In particular, the risk of hypopharyngeal cancer increased with the use of Khaini (OR 2.02, CI 0.81-5.05), Mawa (OR 3.17, CI 1.06-9.53), Pan (OR 3.34, CI 1.68-6.61), Zarda (OR 3.58, CI 1.20-10.68) and Gutkha (OR 4.59, CI 1.21-17.49). A strong dose-response relationship was observed between chewing frequency and the risk of hypopharyngeal cancer (p(trend) < 0.001). An effect of alcohol on cancer of the hypopharynx and supraglottis was observed only among daily drinkers (OR 2.22, CI 1.11-4.45 and OR 3.76, CI 1.25-11.30, respectively). In summary, this study shows that chewing tobacco products commercially available in India are risk factors for hypopharyngeal cancer, and that the potency of Bidi smoking may be higher than that of cigarette smoking for hypopharyngeal and laryngeal cancers.