Pathogen-associated tumorigenesis is a fascinating area of cancer biology. A case study by Muehlenbachs et al. reports a patient with HIV who developed multiple 'tumours', including in the lungs and lymph nodes. Analyses of biopsies from some of these tumours revealed that the cells had similar features to tumour cells, but that they were derived from the common tapeworm Hymenolepis nana. This raises the possibility that some individuals may be misdiagnosed with cancer when they have tapeworm tumours and also raises interesting questions about tumorigenesis.