The
interesting issue for me is the fact that postmenopausal women have
levels of estrogen in their cancers equivalent to those of premenopausal
women despite the fact that premenopausal women have much higher
levels of circulating estrogen. So the issue is where does that
estrogen come from? And what’s interesting or surprising is
that in many tumors, the tumor itself produces either part or all
of that estrogen. And if you look at the relationship between the
amount of estrogen a tumor produces and estrogen receptor positivity,
estrogen receptor-positive tumors are more likely to produce high
levels of estrogen, so it’s like the tumors doing it for itself.
And this data is relevant because a large percentage of the estrogen
in some cancers and in some tumors, all the estrogen in the cancer
comes from in situ synthesis – that’s synthesis
by the tumor itself.
What’s
happening in these tumors with estrogen receptor – they obviously
need the estrogen to keep alive and to grow. And the tumors themselves
developed this ability to be self-maintaining, to make their own
estrogen by taking up circulating androgens and converting it through
the aromatase enzyme to estrogen. So it’s pretty clever by
the tumors, really.
