<span class="citations"><p>Chengjian Mao, "Tamoxifen and 4-hydroxytamoxifen-activated system for regulated production of proteins in eukaryotic cells." U.S. Patent US20030199022, issued October 23, 2003.</p>
</span><a href="https://www.google.com/?tbm=pts#q=20030199022&amp;tbm=pts" rel="noopener" target="_blank">US20030199022</a>