Estimation of the epidermal growth factor receptor by the hydroxyapatite method in human breast cancer.

Results of epidermal growth factor (EGF) receptor in human breast tumours show large variations, mainly due to the lack of standardization of the assays. Our EGF receptor values are higher than those reported previously which may be due to the use of the hydroxyapatite to separate bound and non-bound ligand in a radioligand assay. We found EGF receptors in 58% (103/178) of the tumours (EGF receptor levels: 3 to 625 fmol/mg of membrane protein, mean = 33.3, median = 17.4), with a median Kd of 0.642 nmol/l. There was an inverse correlation between EGF receptors and estrogen receptors (r = -0.215, p = 0.00002, Kendall correlation). There was a difference between EGF receptor content in grade II (mean = 16.9) and grade III tumours (mean = 59.3) (p = 0.027), but not between histopathological types and lymph node status. The relevance of EGF receptor largely depends on the reliability of its determination. The standardized EORTC methodology is a reproducible alternative which will expand EGF receptor determination and permit comparability of data between laboratories.