ESTROGEN FORMATION IN BREAST - CLINICAL AND BIOLOGICAL IMPORTANCE

It has been known for many years that many breast carcinomas can synth esize oestrogens from androgens via the action of the enzyme aromatase . There has been widespread speculation on the possibility that this a cts as an important intracrine source of growth stimulation For exampl e, there are data which indicate that clinical response to aromatase i nhibitors is far more common in tumours which possess measurable amoun ts of aromatase. In addition, aromatase activity in the quadrant of th e normal breast surrounding breast carcinomas is generally higher than in the other quadrants. However, these data are only suggestive and t he case for a significant role for intratumoural aromatase in breast c ancer growth remains unproven. We have recently explored this possibil ity by the transfection of human breast cancer cells with aromatase. B y a series of experiments in athymic mice we have demonstrated that gr owth is supported by this intracrine source in the absence of endocrin e oestrogen stimulation.