Novel 1,3,4-triaza-phenalene and 1,3,4,6-tetraazaphenalene derivatives are disclosed. These compounds inhibit epidermal growth factor receptor (“EGFR”) tyrosine kinase. These compounds and their pharmaceutically acceptable salts and esters have antiproliferative activity and are useful, inter alia, in the treatment or control of cancer, in particular solid tumors. This invention also relates to pharmaceutical compositions containing such compounds and to methods of treating or controlling cancer, most particularly the treatment or control of breast, lung, colon and prostate tumors.