Given our and other existing data on the tumour microenvironment (Dancey and Freidlin, 2003; Fukino et al, 2004), it may be postulated that the high frequencies of stromal EGFR mutations in sporadic and hereditary breast cancers could confound responsiveness to EGFR-TKI and may help explain interpatient variation. The gene discussed is EGFR; the disease is breast carcinoma.