Malignant Transformation of Hymenolepis nana in a Human Host

To the Editor: Muehlenbachs et al. (Nov. 5 issue) 1 describe a case of malignant transformation in a cestode, Hymenolepis nana, and transformation resulting in individual proliferating cells invading host tissues. The authors cite some earlier cases as examples of proliferating parasites that maintained recognizable metazoan tissues. Although their report is mostly accurate, it understates the century-long history of numerous reports of transformations among cestodes that infect humans and other animals, with typically fatal outcomes. Earlier reports used different terminology that is more consistent with invertebrate zoology, such as “aberrant” or “anomalous,” but the developmental and morphologic criteria for neoplasms and . . .