The invention concerns quinazoline derivatives of the Formula I, or pharmaceutically acceptable salts thereof: wherein each of R1, R2, R3, R4 and m are as defined in the description; processes for their preparation; pharmaceutical compositions containing them and their use in the manufacture of a medicament for providing an anti-proliferative effect. The quinazoline derivatives of Formula I are expected to be useful in the treatment of diseases such as certain cancers mediated by erbB receptor tyrosine kinases, and, for example, EGFR tyrosine kinase.