A selective gamma secretase (GS) inhibitor with potential antitumor activity. Gamma secretase inhibitor PF-03084014 binds to GS, blocking proteolytic activation of Notch receptors; Notch signaling pathway inhibition may follow, which may result in the induction of apoptosis in tumor cells that overexpress Notch. The integral membrane protein GS is a multi-subunit protease complex that cleaves single-pass transmembrane proteins, such as Notch receptors, at residues within their transmembrane domains. Overexpression of the Notch signaling pathway has been correlated with increased tumor cell growth and survival.