To further characterise LEFTY1 expression, we stained 140 BO samples from 80 patients, 78 endoscopic biopsies from control sites (oesophagus, gastric fundus and duodenum) in 26 BO patients, and additionally five endoscopic samples from the pylorus, five resected samples of normal colon and five samples of normal oesophagus taken from the proximal part of an oesophagectomy specimen resected for junctional tumours (Supplementary Data 2). The gene discussed is LEFTY1; the disease is bronchiolitis obliterans syndrome.