Morphological analysis of malignancy: a comparative study of transplanted brain tumours.

A comparative study of the cellular composition and ultrastructural features of rat brain tumours produced by early and late passage of neoplastic glial cells was carried out. The cells injected intracerebrally were of a clone neoplastic astrocytes (A15A5) derived from a mixed glioma induced transplacentally by N-ethyl-N-nitrosourea (ENU) in a BD-IX rat. The neoplastic cells were maintained for various lengths of time in vitro and then injected (5 X 10(5) cells) into the left frontal lobe of the brains of syngeneic rats, resulting in a 100% tumour yield. Gliomas produced by cells of earlier passages were less malignant and contained better differentiated astrocytes than those produced by cells of later passages. There were also differences in size, shape, extracellular space, presence of haemorrhage and necrosis, vascularity and invasion of the surrounding tissues. Thus the morphological features of transplanted tumours in vivo correlated well with the in vitro behaviour of neoplastic glial cells.