| abstract |
There is provided compounds of formula (I), wherein R 1 , R 2 , X 1 , X 2 , and X 3 have meanings given in the description, and pharmaceutically-acceptable salts thereof, which compounds are useful as positron emission tomography (PET) imaging agents, useful in the treatment of diseases in which inhibition of epidermal growth factor receptor tyrosine kinase activity or the inhibition of HER2 activity is desired and/or required, and useful in the treatment of cancer. |