We used a pharmacological approach to examine whether exogenous T promotes neurosphere growth through estrogenic or androgenic pathways, employing the specific aromatase inhibitor letrozol and AR antagonist flutamide. These compounds have high specificity, and used in human cancer cell lines show for example, decreased E2 synthesis and anti-proliferative effects of letrozole at concentrations ranging from 10 nM to 100 μM (Bhatnagar et al., 1990; Brogden and Chrisp, 1991; Mitropoulou et al., 2003; Han et al., 2008). The gene discussed is CYP19A1; the disease is cancer.