The immune environment of paediatric solid malignancies: evidence from an immunohistochemical study of clinical cases.

Childhood malignancies are relatively poorly studied in terms of tumour/host interaction. Using tissue arrays of childhood cancers, we analysed immunohistochemical staining for CD68, CD3 and FOXP3 to evaluate infiltration of myeloid cells, lymphocytes and regulatory T cells. Staining for phosphorylated STAT3 was performed in a subset. The majority of paediatric tumours demonstrated a marked infiltration of CD68+ myeloid cells but, with the exception of neuroblastoma, most showed only sparse infiltration of CD3+/ FOXP3- cells. There was evidence for activation of STAT3 in pPNET (50%), ependymoma (45%) and undifferentiated sarcoma (38%), but it was rarely activated in other tumours.