Immunocytochemistry and in situ hybridisation of epidermal growth factor receptor and relation to prognostic factors in breast cancer.

The breast tumour distribution of epidermal growth factor receptor (EGFR) was studied in 193 patients with primary breast cancer by immunocytochemistry on frozen sections. EGFR was correlated (P = 0.0009) with growth fraction assessed by Ki-67, and negatively correlated with oestrogen receptor (ER, P = 0.0001) and progesterone receptor (PR, P = 0.0001) status. In 47 patients, in-situ hybridisation for EGFR mRNA showed good agreement with the immunocytochemically assessed EGFR protein. There were, however, several tumours in which EGFR mRNA could be detected in the absence of EGFR protein and there were differences between the ER and PR status of those tumours in which translation of EGFR mRNA was not seen. The cause of these differences is unclear, but these findings may represent a clue as to the differential control of breast cancer cell receptors.