While CD26 has been shown to have a tumour suppressor effect in melanoma, ovarian cancer, non-small cell lung cancer, prostate cancer, endometrial cancer, neuroblastoma and glioma cell lines, it has been reported to be a marker of tumour aggressiveness in T-anaplastic large cell lymphoma, T-leukaemia, malignant mesothelioma, colorectal cancer and Ewing sarcoma cell lines40,41. Here, DPP4 is linked to malignant mesothelioma.