There is no "comprehensive" database in the US. With 50+ jurisdictions and a nightmarish insurance system I am not surprised. But if you google "metastatic breast cancer database UK" you find this:
"Fifteen breast cancer units across England took part in the pilot for six months from June to November 2011. They identified 598 patients with recurrent and/or metastatic breast cancer, who were then matched with the National Cancer Waiting Times Monitoring Dataset (NCWTMDS) and with data received by cancer registries."
It looks like the UK has been doing exactly what the OP found wasn't happening in the US: centralized databases.
"The Recurrent and Metastatic Breast Cancer Data Collection Project Pilot report" http://www.ncin.org.uk/view?rid=1043
"Fifteen breast cancer units across England took part in the pilot for six months from June to November 2011. They identified 598 patients with recurrent and/or metastatic breast cancer, who were then matched with the National Cancer Waiting Times Monitoring Dataset (NCWTMDS) and with data received by cancer registries."
It looks like the UK has been doing exactly what the OP found wasn't happening in the US: centralized databases.