Two tumour suppressor genes, TRAF7 and CDC42, respectively involved in activation of mitogen‐ activated protein kinases (MAPKs) and in Rho GTPase signalling, were found mutually exclusively mutated in a series of well-differentiated papillary mesothelioma of the peritoneum (35), in absence of the typical mutations of the malignant counterpart, as those involving BAP1, NF2, CDKN2A, ALK, contributing to a clear-cut separation between the two entities. The gene discussed is CDC42; the disease is neoplasm.