GFAP and neoplasm: In addition, GFAP is up‐regulated in non‐neoplastic astrocytes that become reactive in response to the growth of the tumor and do not reflect the differentiation state of neoplastic cells (Gullotta, Schindler, Schmutzler, & Weeks‐Seifert, 1985; Yoshii et al., 1992; H. Y. Yang, Lieska, Glick, Shao, & Pappas, 1993).