Abstract To elucidate the possible roles of proto-oncogenes and growth factors in estrogen-regulated cell proliferation of human breast and gynecologic cancers, we have determined the gene expressions of c-myc, transforming growth factor-alpha and beta 1 (TGF-α, β 1) and epidermal growth factor receptor (EGFR) in a number of these cancer cell lines by using an Intron-Differential (ID) RNA PCR method, which differentially identifies the amplified cDNA from PCR products of genomic DNA contaminants. With this method, we demonstrated the expression of these genes, except EGFR, in an estrogen-dependent breast cancer cell line (CAMA-1). Our results show that TGF-α EGF does not function as an autocrine factor in this cell line. Accordingly, it is unlikely that the TGF-α EGFR system participates as a mediator in the estrogen-induced cell proliferation of CAMA-1 cells. The ID RNA PCR method is a rapid, sensitive and specific technique for mRNA phenotyping and will have great clinical utility.