Immunocytochemical identification of the cells overgrowing tumor cells.

(A) A late passage of classical monolayer cell culture. The majority of cells expressing αSMA is GFAP(−). A small population of GFAP(+)/α-SMA(−) cells is also visible; (B) The cells invaded radially from the spherical core and further grew as monolayer. Three populations were observed: GFAP-positive; αSMA-positive and double negative.