The room temperature powder pattern of lapatinib ditosylate monohydrate (active ingredient in Tykerb used to treat refractory breast cancer) was indexed and the cell from the single crystal X-ray diffraction structure was refined using the experimental capillary data. Unit-cell parameters for the orthorhombic compound with space group Pbca refined from powder diffraction data are a=9.6850±0.0009 Å, b=29.364±0.003 Å, and c=30.733±0.003 Å, α=β=γ=90°, z=8, V=8740.1 Å3. Values of 2θ, d, I, and Miller indices are reported.
