An orally bioavailable, small-molecule gamma secretase (GS) inhibitor with potential antitumor activity. Gamma secretase inhibitor RO4929097 binds to GS and blocks activation of Notch receptors, which may inhibit tumor cell proliferation. 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.