I am using the ketogenic diet to lower my blood and brain glucose levels. So far my body is really happy about it.
Metformin is used a lot for women with PCOS dealing with fertility issues but my sense was that insulin resistance was at play for the development of breast cancer as well. Lots of stage 4 BC sisters are on metformin and tolerating it well. I think if you ask on Inspire.com you might find more.
I think if we think about cancer as a metabolic disease that we are fighting then it makes a lot of sense to switch to a less favorable diet, one that makes cancer grumpy. It has been part of my modus operandi -- making my brain mets uncomfortable
BTW, I found this great article that is very relevant to this discussion:
An integrated multidisciplinary model describing initiation of cancer and the Warburg hypothesis
http://www.tbiomed.com/content/10/1/39
They think glucose dysregulation happens first, then cancer develops.
This also mentions that weekly dosing (metronomic, dose-dense) of certain chemo agents might work better based on cell cycle dynamics.