This paper addresses the expression of the epidermal growth factor (EGF) gene by human breast tumor biopsy samples. Northern analysis was used to demonstrate the presence of an approximately 5-kilobase mRNA which specifically hybridized with radiolabeled human EGF complementary DNA in some human breast tumor biopsy samples. Quantitation of EGF mRNA in 60 human breast tumor biopsies using the RNase protection assay revealed that 83% of tumors contained detectable EGF mRNA. Estrogen receptor (ER) and progesterone receptor (PgR) mRNAs were similarly quantitated in the same samples. It was found that 89.4% of the ER mRNA-positive breast tumor biopsies had detectable EGF mRNA, whereas only 58.3% of the ER mRNA-negative tumors had detectable EGF mRNA. Furthermore, whereas 90.5% of the PgR mRNA-positive tumors contained EGF mRNA, only 60% of the PgR mRNA-negative tumors contained EGF mRNA. x2 analysis indicated that the increased percentage of tumors expressing EGF in the receptor-positive groups was statistically significant (P < 0.01). It was also found that the mean relative level of EGF mRNA in those tumors which were ER and PgR negative [9.8 ± 5.6 (SEM) relative units] was significantly lower than those tumors which were ER and PgR positive (40.5 ± 6.4 relative units, P < 0.05) or ER positive and PgR negative (68.4 ± 19.9 relative units, P < 0.005). These observations suggest that the EGF-expressing tumors probably arose originally from hormonally responsive cell types and that EGF expression in a large proportion of human breast tumors in vivo may also be hormonally responsive.
This work was supported by the Medical Research Council (Canada) and the National Cancer Institute (Canada). L. C. M. is a National Cancer Institute Research Scientist and T. M. is the recipient of a Manitoba Health Research Council studentship.