Despite promising pre-clinical studies with the GSI MK-0752 in NOTCH1-mutated T-ALL cell lines (16, 22), the first phase I clinical trial testing this molecule in patients with T-ALL showed limited antitumor activity, and the continuous dosing regimen was associated with severe gastro-intestinal (GI) toxicity (23). The gene discussed is NOTCH1; the disease is acute lymphoblastic leukemia.