Tamoxifen is more widely known than the aromatase inhibitors such as anastrozole. Is anastrozole a more modern medication for chemoprevention of breast cancer? Dr. Anton Titov, MD.: How should the consideration be given? So, first of all, aromatase inhibitors really can't be used in premenopausal women. Dr. Marc Lippman, MD.: But the overwhelming majority of breast cancers are in postmenopausal women. So that's not a huge problem. You can't use aromatase inhibitors in premenopausal women because you have functioning ovaries. If you reduce estrogen concentrations with an aromatase inhibitor, gonadotrophins go up. Then you stimulate a functional ovary, and you make more estrogen, so you overcome the block. You can't do that in a postmenopausal woman because her ovaries don't work anymore. So her rising gonadotropins don't increase your estrogen concentrations. So aromatase inhibitors are primarily used in postmenopausal women. Now, Tamoxifen does rarely has some toxicities that are worrisome. thrombosis and occasionally pulmonary embolus. Now that's a serious side effect. No question about it. Dr. Marc Lippman, MD.: But if you screen patients to find patients who have had previous histories of thrombi, who are inactive, who have obesity, you can use Tamoxifen reasonably safely. One woman in 150 who takes Tamoxifen for five years will develop low-grade endometrial cancer readily treated by hysterectomies. Now, if you're a normal person and you don't have any risks at all, and someone tells you a drug might cause endometrial cancer, you know, you might say I'll have nothing to do with it. Dr. Marc Lippman, MD.: But of course, that has a risk-benefit ratio. If you can reduce your risk of a lethal disease, breast cancer, by 50%, you run half of the endometrial cancer. Obviously, if you're playing the odds, it's what you would do here. Dr. Marc Lippman, MD.: But most people don't play odds like that correctly. They just get afraid and don't do things. So for postmenopausal women, it's Tamoxifen versus anastrozole at this point. For premenopausal women, Tamoxifen does work as a chemoprevention agent that was proven in two huge studies involving, as I said, north of 10,000 patients. The risk of breast cancer is much lower in women under the age of 50 than we think. Tragically it's a premenopausal breast cancer. The median age of breast cancer is 56 years of age. Most patients are postmenopausal. Dr. Marc Lippman, MD.: But there are remarkable benefits in these prevention clinical trials, which had been followed up for many years. Five years taking Tamoxifen, the protection persists for So in many cases, you might say this. Why don't we wait till women are postmenopausal and then give them an aromatase inhibitor, which is more effective? You are going to be preventing most breast cancer. And that makes sense to me too. I would take half a loaf here. These aromatase inhibitors just aren't widely used to prevent breast cancer. And it's very unfortunate because breast cancer is still the most common malignancy of women overwhelmingly, and then the morbidities associated even with non-invasive breast cancer are substantial.