TERT and meningioma: However, while Ben-Men-1 proliferated rapidly in vitro, orthotopic xenografts using this cell line grew slowly, making it suboptimal for testing therapeutic agents.367 Furthermore, introducing alterations such as the human TERT gene or disruption of p53 and pRb pathways necessary to immortalize meningioma cell lines may also alter how closely these cell lines recapitulate their tumor of origin.368