Hi - I heard about this when I was first diagnosed too and investigated further. The quick answer is that when humans drink milk, it causes a rise in the amount of insulin-like growth factor I (IGF-I) in the bloodstream. IGF-I is a powerful stimulus for cancer cell growth. When breast cancer cells are mixed with IGI-I in a test tube, for example, they grow rapidly.
A great resource for learning more about this (and the role of nutrition and cancer in general) is The Cancer Project (
www.cancerproject.org). I took a free cooking class sponsored by this organization at UCSF and I learned a ton about the role of dairy, meat, etc in cancer. They've got a great book out called "The Survivor's Handbook - Eating Right For Cancer Survival" that explains all of these things and backs it up with citations to scientific studies. Plus there are great recipes.
My husband and I have switched to a mostly vegan diet based on what we learned from The Cancer Project. Of course, I do enjoy the occassional cheese piece now and again ;-)