Vildagliptin‐induced ground‐glass nodules mimicking lung metastases in a cancer patient receiving Lactobacillus probiotic supplementation

The association between gut microbiota and the lung immune system has been attracting increasing interest. Here, we report a case of pancreatic cancer in which the dipeptidyl peptidase‐4 inhibitor vildagliptin induced unusual manifestations of interstitial pneumonia, possibly under the influence of Lactobacillus paraplantarum probiotic supplementation. Chest computed tomography and positron emission tomography showed multiple ground‐glass nodules (GGNs) mimicking metastatic lung cancer. Transbronchial biopsy specimens showed mild fibrosis and infiltration of lymphocytes consisting of more CD4+ than CD8+ cells. The CD4+ cells did not include FOXP3+ regulatory T cells. Bronchoalveolar lavage confirmed lymphocytosis with a markedly increased CD4+/CD8+ ratio of 7.4. The nodules disappeared shortly after vildagliptin and probiotics were withheld. If unusual interstitial pneumonia is observed in some cancer patients, physicians should pay careful attention to their medication history, including probiotic supplements.