PURPOSE: In a phase III study of gemcitabine plus erlotinib for advanced pancreatic cancer conducted in Canada, the incidence of interstitial lung disease (ILD) was 3.5 %. However, the incidence of ILD was reported as high as 8.5 % in a Japanese phase II study. These results suggest the influence of ethnic factors in the association of the use of gemcitabine plus erlotinib with the incidence of ILD. Here, we conducted a prospective study to analyze the relationship between human leukocyte antigen (HLA) alleles and ILD in Japanese patients with advanced pancreatic cancer receiving gemcitabine plus erlotinib. METHODS: Patients were treated with gemcitabine (1000 mg/m(2); administered by intravenous infusion on days 1, 8, and 15 every 4 weeks) and erlotinib (given orally at 100 mg/day). We compared the frequencies of HLA alleles in patients who did and did not develop ILD. RESULTS: A total of 57 patients were treated, and 4 patients (7.0 %) developed ILD. The combination of HLA-B*15:01 and DRB1*15:01 was observed in 2 of 4 patients (50 %) with ILD and in only 1 of 53 patients without ILD (2 %) resulting in odds ratio of 52.0 (95 % CI 3.2-842.5; p = 0.011). CONCLUSION: These results suggest that the combination of HLA-B*15:01 and DRB1*15:01 is associated with ILD in Japanese patients with advanced pancreatic cancer receiving gemcitabine plus erlotinib.