Hi Lolly,
Broccoli also contains DIM and I3C, two anto estrogen chemicals. I3C metabolizes into DIM (the active compound) is available in most health food stores. DIM has been shown to active augment the effacy of tamoxifen. Some people prefer DIM supplementation over I3C because I3C may activate dioxin receptors and isnot recommended for people living near refineries of petro-chemical plants.
Here are some links:
http://www.annieappleseedproject.org/dimsafin.html
Here's 35 (yes, 35) short technical summaries of it's actions:
http://www.integratedhealth.com/infoabstract/i3cab.html
Al