Thus, the observed differences between primary tumour and metastasis may be explained by a trend in favour of gene or protein expression deregulation when the alteration is acquired by metastatic cells, whereas by a clone, present in a subgroup of primary tumour cells and characterised by an EGFR-independent metastatic phenotype, when the alteration is limited to primary tumour cells. The gene discussed is EGFR; the disease is neoplasm.