These effects are attributed to the release of soluble factors like heparanase, IL6, TNF, and IL1 by astrocytes, which stimulate metastatic determinants like endothelin-1 receptor expression, ERK phosphorylation, and induction of survival genes like BCL2L1 and TWIST1 in tumor cells.80,83–86 Astrocytes also regulate immune response within the brain during BrM progression. The gene discussed is BCL2L1; the disease is neoplasm.