Neoplasms in proteus syndrome

We report on 2 children with Proteus syndrome who developed neoplasms. Patient 1 had a probable mesothelioma, although papillary carcinoma of the thyroid could not be completely ruled out. Patient 2 had bilateral ovarian serous cystadenomas with nuclear atypia. Other unusual neoplasms in Proteus syndrome are discussed, together with their etiologic and pathogenetic possibilities.