Single cell sequencing on pediatric sialoblastoma

As a rare embryonal malignant tumor, sialoblastoma recapitulates primitive salivary gland anlage, usually locating in parotid or submandibular gland and diagnosed at birth or during infancy. The transcriptome profiles as well as intertumoral heterogeneity of sialoblastoma have not yet been investigated. Here, through single-cell RNA sequencing of tumor samples from the same patient before and after chemotherapy, we constructed the first cell transcriptomic atlas of sialoblastoma. By calculating differentially expressed genes and performing gene ontology analysis, we found downregulation of cell proliferation while upregulation of epidermic differentiation pathways after chemotherapy. In addition, we demonstrated distinct transcriptional programs embedded in tumor, including cycling cells, basaloid cells, ductular cells, myoepithelial-like cells and transitional states. The proportion of cycling cells and transitional state cells decreased after chemotherapy whereas the proportion of basaloid cells and myoepithelial cells increased. Taken together, we offered a valuable resource for deciphering cellular heterogeneity as well as adaptive change of tumor cells after chemotherapy, providing insights into clinical management of sialoblastoma. A 6-month-old infant with growing left-sided firm cheek mass was referred to our institution and diagnosed as sialoblastoma through fine needle biopsy and following pathological examination. After four cycles of neoadjuvant chemotherapy adopting intermediate-risk neuroblastoma regimen (carboplatin, cyclophosphamide/etoposide, and doxorubicin), the volume of tumor did not shrink significantly.  We obtained the tumor tissue from the same  patient before and after chemotherapy ,and performed single-cell sequencing.