EGFR and neoplasm: Although the low toxicity observed suggests that greater doses may be tolerated, it may be difficult to standardise the amounts of active drug in these patients Surrogate markers of systemic anti-EGFR activity such as development of rash or diarrhoea do not define activity in the tumour, but may represent a minimal level of activity and have been correlated with treatment response in some trials [34,52,53].