Gift,
There is no strong evidence suggesting a link between caffeine and breast cancer (but have been some small studies showing possible link warranting further review). Caffeine does appear to impact breast health in regards to fibrocystic breast disease (increased pain, swelling) but studies have not demonstrated a connection with BC risk. However, caffeine certainly impacts many areas of health (blood pressure, insomnia, anxiety, etc). I feel comfortable with patients enjoying a cup of coffee but don't like them drinking it all day. Here are a few studies from PubMed.
http://www.ncbi.nlm.nih.gov/pubmed/20680436
http://www.ncbi.nlm.nih.gov/pubmed/18852405