The invention provides a compound for use in the treatment of T-Cell Acute Lymphoblastic Leukaemia (T-ALL), the compound having the formula (1):or being a pharmaceutically acceptable salt thereof； wherein:n is 0, 1 or 2；Ar1 is selected from an optionally substituted phenyl, pyridyl, thienyl and furanyl；Q1 is selected from C(═；O), S(═；O) and SO2；A is absent or is NR2；R1 is selected from:hydrogen；an optionally substituted C1-6 non-aromatic hydrocarbon group； andoptionally substituted 3- to 7-membered non-aromatic carbocyclic and heterocyclic rings containing one or two heteroatom ring members selected from O, N and S, and bridged bicyclic heterocyclic rings of seven to nine ring members of which one or two are nitrogen atoms, the carbocyclic and heterocyclic rings and bridged bicyclic heterocyclic rings；R2 is selected from hydrogen and C1-4 alkyl； orNR1R2 forms an optionally substituted 4- to 7-membered non-aromatic nitrogen-containing heterocyclic ring optionally containing a second heteroatom ring member selected from nitrogen and oxygen.
