Indoor air pollution from solid fuels and risk of hypopharyngeal/ laryngeal and lung cancers: A multicentric case - Control study from India

Background: A recent monograph by the International Agency for Research on Cancer (IARC) has identified indoor air pollution from coal usage as a known human carcinogen, while that from biomass as a probable human carcinogen. Although as much as 74% of the Indian population relies on solid fuels for cooking, very little information is available on cancer risk associated with these fuels in India. Methods: Using data from a multicentric case-control study of 799 lung and 1062 hypopharyngeal/laryngeal cancer cases, and 718 controls, we investigated indoor air pollution from various solid fuels as risk factors for these cancers in India. Results: Compared with never users, individuals who always used coal had an increased risk of lung cancer [odds ratio (OR) 3.76, 95% confidence interval (CI) 1.64-8.63]. Long duration of coal usage (>50 years) was a risk factor for hypopharyngeal (OR 3.47, CI 0.95-12.69) and laryngeal (OR 3.65, CI 1.11-11.93) cancers. An increased risk of hypopharyngeal cancer was observed among lifelong users of wood (OR 1.62, CI 1.14-2.32), however this was less apparent among never-smokers. Increasing level of smokiness inside the home was associated with an increasing risk of hypopharyngeal and lung cancer (P_trend< 0.05). Conclusion: This study showed differential risks associated with indoor air pollution from wood and coal burning, and provides novel evidence on cancer risks associated with solid fuel usage in India. Our findings suggest that reducing indoor air pollution from solid fuels may contribute to prevention of these cancers in India, in addition to tobacco and alcohol control programs.