The biological effects of oestrogen are mediated by two distinct oestrogen receptors, alpha and beta, and these exist in both sexes.[27] These receptors often exert opposite effects on cellular processes that differentially influence the development and the progression of cancer.[28] The oestrogen receptor alpha, of particular relevance in this study, is associated with aberrant proliferation, inflammation and cancer development.[28] The finding of an association between SNPs in the gene coding for the oestrogen receptor alpha and an association to BO is therefore interesting. The gene discussed is ESR1; the disease is bronchiolitis obliterans syndrome.