Expression of Concern: Characterization of Stem-Like Cells in Mucoepidermoid Tracheal Paediatric Tumor

After this article [1] was published, questions were raised about whether there was adequate evidence to support claims about the nature of cells used in the study; about the reliability of results for which supporting data were not reported in the article; and about the source(s) and ethics approval(s) in place to support work with human bone marrow-derived mesenchymal stromal cells (BM-MSCs).PLOS followed up on these issues in accordance with Committee on Publication Ethics (COPE) guidance.The corresponding author could not be reached in these post-publication discussions, but co-authors provided some supporting data and clarifications as outlined below. Evidence to support claims that cells used in this study were cancer cells, and that there are specialized stem cell-like cells in the tumorA member of PLOS ONE's Editorial Board advised that PCR and karyotype analysis data would be needed to support claims about the nature of the cells used in the study, and that without these data the article's conclusions are not adequately supported.PCR data were not provided to confirm the t(11;19) (q21;p13) translocation in the primary tumor cells, and the PCR method and reagents used were not reported in sufficient detail to enable replication.The authors noted that the tumor diagnosis was provided by pathologists, and that information on the mutation was reported in the article as background information about the materials used but was not intended as a primary result of the reported study.The authors also commented that PCR analysis to confirm the translocation was performed by the Department of Pathology and Cytology, Karolinska University Hospital, and that the dataset is retrievable from the hospitals archived pathological-anatomical diagnosis data repository but cannot be made publicly available due to patient privacy considerations.Questions were raised about differences between PCR results obtained for the primary tumor and the karyotype of MEi cells isolated from that tumor.The authors commented that this may be due to genetic drift.The consulted member of the Editorial Board advised that they were satisfied with this response.The authors provided image data (S1 File and S2 File) to support the statement, "microscopical analyses (FISH analysis using a probe specific for human X/Y chromosomes) were negative; indicating that MEi cells did not propagate in vivo."They also stated that negative FISH findings cannot prove a lack of cellular growth other than in the particular section studied, and noted that the statement, "Mei cells did not form teratomas," was based on visual inspection, palpation, and FISH analysis.