ABSTRACT
Estrogens enter tumor cells by passive diffusion and bind with high affinity and specificity to estrogen receptors. Estrogen receptors are ligand-activated; the interaction of the ligand-receptor complexes with DNA occurs at special transcription-activating nucleotide sequences, referred to as estrogen-responsive elements that lie within the respective promoter regions. The expression of estrogen receptors in mammary carcinomas indicates advanced functional differentiation within the tumor accompanied by a high degree of morphological differentiation. The good quantitative correlation between in vitro measurements of estrogen receptor concentration and in vivo PET readings could be reproduced in McGuire's next study performed by the same research group on patients with metastases of a mammary carcinoma. Few patients exhibited an axillary metastasis, although both retrosternal and parasternal foci of activity were revealed by scintigraphic imaging in isolated cases. The use of modern multihead camera systems can also be expected to improve the photon yield.
