Background Epidemiological studies have repeatedly found lower risks of lung cancer in farmers. Besides a lower prevalence of tobacco-smoking, exposure to endotoxins, which is highly present in animal farming, has been offered as an explanation. However, its role remains controversial. Little is known about the agricultural activities concerned. In the AGRICAN cohort, we assessed the relationship between animal farming and lung cancer by investigating the type of animals, tasks, timing of exposure and taking smoking history into account.

Methods The AGRICAN cohort consisted of 170,834 participants affiliated to the French agricultural health insurance scheme. Linkage with cancer registries identified 487 incident lung cancers from enrolment (2005–2007) to 2011. The enrolment questionnaire provided detailed information on lifelong farming, including tasks performed with cattle, horses, pigs, poultry, sheep and/or goats with years of beginning and end, and exposure to a farm during the first year of life. Associations between lung cancer and exposure to animals were analysed using a Cox model with adjustment for smoking, using age as time scale.

Results Risk in lung cancer (especially adenocarcinoma) was inversely associated with duration of occupational exposure to cattle (≥40 years: HR = 0.60, [95% CI=0.41–0.89], p–trend = 0.04) and horse (≥20 years: 0.64 [0.35–1.17], p–trend = 0.08), but not with poultry or pig farming. Lower lung cancer risk remained associated with long–term exposure to cattle, even 25 years after cessation of exposure. More pronounced decreased risks were observed among individuals who had cared for animals, undertaken milking and who had been exposed to cattle in infancy.

Interpretation Our study provides strong evidence of an inverse association between cattle and horse farming, and lung cancer. Further research is warranted to identify the etiologic protective agents and biological mechanisms involved.