ESR1 and breast carcinoma: Levels of the marker transcripts AREG, GATA3, TFF1 and PGR were positively influenced by PCE1 (P < 0.05, Fig. 2) indicating the direct quantitative role of intratissue estrogen levels on ESR1 activation in the glandular tissue and stressing the relevance of the increase in intratissue estrogens levels associated with breast cancer risk factors.